Fishikaint :
I was thinking of getting a wifi repeater but I found out it makes your Internet slower but the signal stronger, so then I heard of wifi boosters and didnt know what they do.
Most WiFi is far faster than most ISPs, so a repeater makes the WiFi slower, it doesn't necessarily make the internet slower. But it also depends on what you want to do in the internet.
What WiFi has and a repeater will exaggerate is high latency of your internet connection. That is the time between when the computer sends a signal and the response arrives back. If you are shoot-em-up gaming, this equals a quick death. If you are web browsing, it may not matter. For streaming video, speed is more important than latency, so strengthening your WiFi connection is likely to help.
If you are operating at the outside of the range, buy good equipment rated for higher speeds so when performance lags, you will still get acceptable service. And buy from a place with a good return policy so if the equipment doesn't do what you need, you can try something else. That what the policy is there for.