Assalamu alaykum.I'm am new to islam and i'm not well grounded with her rules.Please,what I want to know is that sometimes I am unable to complete Al-fatiha behind an imam even though I begin the salat with him.Please,what would i do?
Also,the same situation usually happens with the second tashahhud.JAZAKUMU LAH KHAYRAN!

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

First of all, we praise Allah, Almighty, for having guided you to Islam and we ask Him to make us and you firm and steadfast on it until we die.

As for your question, if the Imam performs Rukoo’ (bows down) before you complete the recitation of Al-Faatihah, then complete its recitation and then catch up with him while he is still in Rukoo’, and if you perform Rukoo’ with him and not complete Al-Faatihah, then there is no harm on you.

As for the last Tashahhud in the prayer, its end is “I bear witness that Muhammad is His Servant and His Messenger.” As for what follows it, which is the Abrahamic prayer, then if you mean that you do not finish the last Tashahhud before the Imam concludes the prayer with Salaam, then do not say the Tasleem [saying Assalaamu Alaykum to finish the prayer] along with the Imam, but complete the Tashahhud, and then say the Tasleem.

Kash-Shaaf Al-Qinaa’, one of the Hanbali books, reads:

“With regard to the Tashahhud, if the Imam precedes the congregation in reciting it, then the person led in prayer does not follow him; rather, he completes the Tashahhud if his Imam says the Tasleem, then he says the Tasleem; this is for the general commands about (completing) the Tashahhud.” [End of quote]

However, if you mean that you do not complete the Abrahamic prayer before the Imam’s Tasleem – while you complete the Tashahhud – then it is sufficient for the Abrahamic prayer to say “O Allah! Send prayers upon Muhammad”, according to those who say that it is a pillar.

So, when the Imam says the Tasleem, it is enough to say “O Allah! Send prayers upon Muhammad”; then say the Tasleem along with the Imam and it is not an obligation on you to say its complete formula: “O Allah! Send prayers upon Muhammad and the followers of Muhammad, just as You sent prayers upon Ibraheem ………”

For more benefit on the shortest form of Tashahhud and its different wordings, please refer to Fataawa 371557, 322516 and 375343.

For more benefit on the merits of Islam, please refer to Fataawa 85456 and 102075.

For more benefit that Islam is from Allah, please refer to Fataawa 88176 and 85234.

For more benefit on the comprehensiveness of the religion of Islam, please refer to Fataawa 81929, 86091 and 82057.

For more benefit that Islam is the religion of all the Prophets, please refer to Fataawa 81979, 88906 and 88051.

For more benefit that everything in the universe testifies that Islam is the true religion, please refer to Fatwa 111063.

For more benefit on the branches of Faith, please refer to Fatwa 107210.

Allah knows best.