Question

How to convert English sentences into sanskrit

Answer 1

First find the translation for the verb using the purusha (person) and the vachanam (number).
Then, find the correct words for the nouns using shabd roop.
 That's it. 
To become better at translating, you just need to practice. That way, you become more confident, you improve vocabulary and memorise the dhatu and shabd roop.

Hope I helped.

Answer 2

To translate English in sanskrit you should know words of sanskrit. You should learn dhatu rup etc, then you will translate English in sanskrit.