Turning my PC into a decent gaming rig, suggestions?

I was going to start selling my other laptop and my xbox one and try to save up for a whole new gaming pc to build, but someone told me I should just put a good graphics card in my desktop I already have ( a lenovo k450e i5 with 8gb ram and 1tb of hd but no SSD) that me and my dad use for simple stuff like YouTube and school stuff. I figured it'd be a lot cheaper and a pretty good idea, I was thinking of just putting a new around 250$ nvidia card in there and buy around 200 gba of SSD, do you think that'd be good for me just running games like h1z1 and rust at high settings? And any suggestions on any parts I should throw in as well?

Read more: Turning my PC into a decent gaming rig, suggestions?