how do you separate 5ghz wifi from 2.4 gh

If your Wi-Fi router supports it, you set up two different networks one for 5 and one for 2.4

Some routers allow you to use the same name where it’ll be treated as the same, and there is no way to identify the difference without connecting, or you can give them different names

What do you mean by that? It depends on your router or access point which frequencies and channels are supported. There may or may not be separate SSID for 5 vs 2.4GHz. If that is the case, you can name them in a way that makes clear which is which, and then you can can choose to which you want to connect. For example, me5 and me2.4