OK - so first thing, if you don’t know what you’re doing get an electrician. You have a two gang box - handling two loads. One of those loads is a three way - linked to the switch in the other box.
Step 1 - NEVER trust wire colors. You need to identify the Line (from the breaker Box) Load (to the device) the Neutral (back to the breaker box neutral) and ground for each switch As well as the ‘traveller’ that links the light in your two gang (double plate) box with the single gang light switch.
Once you know what these are use this post to figure out what goes where:
If that reads like greek - please get an electrician.
On the matter of the 2nd light switch by itself, with GE devices, you cannot use ‘any old switch’ as the remote - it MUST be a GE Add-on switch. Thus why i say you need to get one.