I also wanted to ask you how must the ruku and sajda be performed? For example in Rukku to what extent one should be bended
Or in Sajda is it okay if my elbow touches my knees ?

For rukuu, one must bow to the extent that the fingers reach the knees.
For sujood, there are 7 parts of the body which is wajib for them to touch the ground that is the forehead, two palms, two knees and the two big toes. As for the elbows touching the knees in sajda, there is no problem