Praise be to Allaah.
If you are referring to the ritual bath of ghusl, then the answer is as follows:
Al-Bukhaari reported in al-Saheeh (248) from Aaishah that when the Prophet (peace and blessings of Allaah be upon him) did ghusl to purify himself from janaabah (impurity following intercourse), he would start by washing his hands, then he would do wudoo as for prayer, then he would dip his fingers into the water and make the water reach the roots of his hair, then he would pour water over his head three times, scooping the water up with both hands, and then he would pour water over his entire body.
Al-Haafiz said in al-Fath (1/248): he would start by washing the parts of the body ordinarily washed in wudoo in order to honour them, and so as to include both kinds of purification, the minor and the major
Al-Haafiz also said (1/362): Al-Bukhaari also understood this to mean that it is waajib when making ghusl to purify oneself from janaabah to wash oneself once, and that the one who does wudoo with the intention of making ghusl and then washes the rest of his body does not have to repeat his wudoo if he does not do anything to break it [e.g., pass wind, etc.]
Ibn Qudaamah said in al-Mughni (1/217): There are two ways of making ghusl to purify oneself from janaabah, one of which is sufficient, and the other is the perfect way. What al-Khiraqi mentions here is the perfect way. Some of our companions said: the perfect way includes ten things: the niyyah (intention), saying Bismillah (In the name of Allaah), washing the hands three times, washing away whatever dirt is there, doing wudoo, pouring water over the head three times making sure that it reaches the roots, pouring water over the rest of the body, starting on the right side, rubbing ones body with one's hand and moving from the place where one has done ghusl in order to one's feet. It is mustahabb to make sure that the water reaches the roots of the hair on one's head and beard before pouring water over them. Ahmad said: Ghusl to purify oneself from janaabah should be done in the manner described in the hadeeth narrated from Aaishah, who said: When the Messenger of Allaah (peace and blessings of Allaah be upon him) did ghusl to purify himself from janaabah (impurity following intercourse), he would start by washing his hands three times, then he would do wudoo as for prayer, then he would run his fingers through his hair until he thought the water had reached his scalp, then he would pour water over his head three times, scooping the water up with both hands, and then he would wash the rest of his body. (Agreed upon). Maymoonah said: The Messenger of Allaah (peace and blessings of Allaah be upon him) did wudoo to purify himself from janaabah, then he poured water on his hands and washed them two or three times, then he poured some water from his right hand into his left, and washed his private parts, then he struck his hand on the floor or wall two or three times, then he rinsed his mouth and his nose, and washed his face and forearms, then he poured water on his head, then he washed his entire body, then he moved slightly and washed his feet. Then I brought him a cloth, but he did not want it, and he started to wipe the water away with his hands. (Agreed upon). A lot of the requirements (of ghusl) are listed in these two hadeeth. Beginning on the right is important because the Prophet (peace and blessings of Allaah be upon him) liked to always start on the right when purifying himself. According to a hadeeth narrated from Aaishah, when the Messenger of Allaah (peace and blessings of Allaah be upon him) did ghusl to purify himself from janaabah, he would call for something like a milking-vessel, and he would take some water in his hands, then he would start with the right side of his head, then the left. Then he would take some water in his hands and start pouring it over his head. (Agreed upon). With regard to washing the feet after doing ghusl, there was some dispute as to what Ahmad actually said. According to one report, he said, I would rather wash them (the feet) after doing wudoo, because of the hadeeth of Maymoonah. According to another report, he said, We should act according to the hadeeth of Aaishah, which says that he did wudoo for prayer before doing ghusl. And Allaah knows best.
He said: If he does ghusl once and makes water reach every part of his head and body, and does not do wudoo, that should be sufficient if he rinses his mouth and nose and has the intention to do ghusl and wudoo, but in this case is not doing that which is better.
What is mentioned here is what is sufficient, but the perfect way is preferable, which is why he said he is not doing that which is better i.e., if he does no more than that, this is sufficient even though he is not doing what is perfect and preferable. The phrase has the intention to do ghusl and wudoo means that ghusl is sufficient for both if he has the intention for both. This is what was stated by Ahmad. Another opinion was also narrated from him, which is that ghusl is not sufficient for wudoo unless he does wudoo either before or after ghusl. This is also one of the two opinions of al-Shaafai, because the Prophet (peace and blessings of Allaah be upon him) did that, and because both janaabah (major impurity) and hadath (minor impurity) are present, and purification from both is required.
Allaah says (interpretation of the meaning):
approach not al-salaah (the prayer) when you are in a drunken state until you know (the meaning) of what you utter, nor when you are in a state of janaabah (i.e., in a state of sexual impurity and have not yet taken a bath) except when travelling on the road, till you wash your whole body [al-Nisa 4:43]
So the lack of ghusl has been made the factor that prevents a person from praying, and if a person has done ghusl, he has no reason not to pray. Both are acts of worship of the same type. In ghusl a lesser type is incorporated in a major type, as umrah is incorporated in Hajj.
Ibn Abd al-Birr said: The one who does ghusl to purify himself from janaabah, if he does not do wudoo but he makes water reach every part of his body, he has done what is required of him, because Allaah has enjoined upon the one who is in a state of janaabah to do ghusl, not wudoo, when He says (interpretation of the meaning): if you are in a state of janaabah (i.e., had a sexual discharge), purify yourself (bathe your whole body. [al-Maaidah 5:6]. This is the consensus of the scholars and there is no dispute among them; they are agreed that it is mustahabb to do wudoo before doing ghusl, in emulation of the Messenger of Allaah (peace and blessings of Allaah be upon him) and because this reinforces and perfects ghusl.
And Allaah knows best.