I have a Lenovo H50 desktop and I'm thinking about upgrading my graphics card, I've got a 300 dollar budget?

I also can't tell what my power supply can take or whatever but I found this in a manual.
Some: 180 watts, autosensing, universal (100V-240V)
Some: 180 watts, autosensing, 85% PSU, EnergyStar 6.0, universal (100V-240V)
Some: 280 watts, autosensing, universal (100V-240V)
Some: 280 watts, autosensing, 85% PSU, EnergyStar 6.0, universal (100V-240V)
Not sure what any of this means.

The first step of a PC upgrade is determining each of the parts of your PC, and then, you can ask the best upgrade for a gaming improvement if that is what you are looking for.
Lenovo is a brand. H50 is basically a computer case.
You are going to have to eventually open up your pc, so get some practice.

First, Install Speccy and Belarc Adviser. They will read a certain amount of the hardware.
Every pc consists of
CPU, CPU Cooler, Motherboard, dram, Storage (Hdd, ssd as applicable, Video Card or graphics processor, case, Power Supply, Optical Drive, Operating System, Display
http://pcpartpicker.com/parts/partlist/
https://www.piriform.com/...com/speccy
http://www.belarc.com/...nload.html

Need to understand the power supply and system power draw or it gets replaced also in the upgrade.
Your cpu also is a factor in gaming and how strong a graphics card to pair with it.

Shut down, open the case, read and record the power supply information.
Measure length of a graphics card that could plug into a pcie x 16 slot.

Would prefer to avoid recommendation without knowing the details to answer correctly.

H50 install SSD