So when i start up unity i enter the fps microgame template at the scene place it runs about 100 fps but when i start up the game it ridiculously lags at an point it crashes idk why that happens i have a 8gb ram?
First, 8gb of RAM is a pretty tiny amount, but also you’re not really giving us much information to go on here. What version of Unity are you using? Do any errors pop up in the console? What point does it crash at?
I am using the 2020.3 the problem is that when i start up the game it literally crashes withn some seconds
if 8gb of ram isnt enough then how much i need?
alr so i checked my task manager when i looked at my ram it dint even pass 7gb of ram? maybe is my cpu that bad, i have a 3 Ghz if you cant help me out its ok! i can manage to make my own with the asset store
As asked by murgilod, what errors pop up? Just saying “it literally crashes” does nothing to help us help you 
We need as much information as you can provide, so please dont hold back.
Secondly, you should really post this in another forum section as you would be more likely to get reponses from team members that worked on the fps microgame. One of the sections in here: https://forum.unity.com/categories/teaching-certification.101/
Thirdly, it only uses 7GB ram as unity will max out whatever ram you have to a point. If you had 32GB you would see it go way over 8gb, but as you only have 8gb it cannot and so its capping itself, at likely the cost of performance etc.
To be honest 8GB is not really enough for anything these days, you should consider buying an extra RAM stick as an 8GB stick is very cheap and easy to install (it literally slots in). This will help not only with unity but performance on your OS, all apps, internet browsing etc.
@hippocoder or @zombiegorilla maybe you can move this to the relevant section so OP can get targeted help? (I did this as a new reply as I wasnt sure if editing my pervious one with @'ing you guys in would actually give you a notification or not, so feel free to delete this reply if you want )