Psychology of chess

It`s the 3rd year that i learn to play chess but I have some difficulties : it seems difficult for me to learn all these variations of an opening because I haven`t found the right way to do it yet.

Furtherly, having won a piece and / or some pawns, I can`t win because I feel anxious !!!

Finally, I`ve lost many games seeing my " flag " down !!!

Can somebody help me?