Praise be to Allah.
You should note, may Allaah guide you, that this religion is a religion of ease, as the Prophet (peace and blessings of Allaah be upon him) said: “Religion is very easy and whoever overburdens himself in his religion will not be able to continue in that way. So you should not be extremists, but if you cannot be perfect, then try to be near to perfection and receive the glad tidings that you will be rewarded; and what helps you to persist in worship is to do it at times when you have most energy, such as at the beginning of the day, after the sun has passed its zenith and at the end of the night.” (Narrated by al-Bukhaari in his Saheeh, no. 39).
If a person cannot read and write, then he has to learn what he should say in his prayer, and how to pray. The fact that he cannot read or write does not mean that he is unable to do that, because that is easy, praise be to Allaah. Most of the Sahaabah could not read or write, but they were able to pray well.
But if a person says, someone may be new in Islam, and if he wants to learn what he should say in his prayer, he needs time; the same applies if he is unable to memorize al-Faatihah. So how should he pray?
The answer is: He should pray, and when he comes to the place where Qur’aan is to be recited, he should glorify Allaah, praise Him, magnify Him and proclaim His Oneness, i.e., he should say Subhaan Allaah, wa’l-hamdulillah wa Allaahu akbar wa laa ilaaha ill-Allaah (Glory be to Allaah, praise be to Allaah, Allaah is Most Great and there is no god but Allaah).
The evidence for that is the saheeh hadeeth narrated from Rafaa’ah ibn Raafi’ – the hadeeth about the one who did not pray properly – according to which the Messenger of Allaah (peace and blessings of Allaah be upon him) said to him: “If you have memorized some Qur’aan, then recite it, otherwise praise Allaah, glorify Him and proclaim His Oneness).” (Narrated and classed as hasan by al-Tirmidhi, al-Jaami’, no. 302. Also narrated by Abu Dawood in his Sunan, no. 858; classed as saheeh by al-Albaani, see Saheeh Abi Dawood, no. 767).
And Allaah knows best.
See Subul al-Salaam, 1/255-256.