I was at a softball game and when i went for a slide i slid wrong and on the left side of my knee something doesn't feel right when i walk?

Ice it: Elevate it. Compress it if you feel you need to and take some ibuprofen . If not improving get an evaluation

Probably ok: You probably have some contusion, or ligament strain. Studies show that if you are under 55, can walk at least 4 steps, no point tenderness on the kneecap or on the outer side, & can flex your knee to 90 degrees , then there is no need for x-rays. This only means there is probably no fracture, but there maybe damage otherwise. You should go to the ER if symptoms don't improve in 2 days