Step one: Kill power to what you are working on. Then you wont get electrocuted...

The red is a traveler for a 3 way switch. The switch you are installing would need 3 way capability if you want everything to work the way it used to. You may need to keep the other switch that activates this light on or off for this new switch to work if you choose to install it as is (unless it can do 3 way). Considering safety reasons, it is not be wise to not have a 3 way, the other switch is there for a reason, allowing light for safe passage of the room in the dark.

One black is your incoming power and one black goes to/from the light. The whites need to be all connected. Does your current switch have wires coming out of it or a place to put a white. If it has its own white wire, connect that to the others. If it doesnt have its own wire you need to take scrap wire (correct gauge size) and get a white from it and use that to connect to the others.

If this is all over your head, stop and get a switch that does 3 way and hire out.

There are too many things going on in that box for a self-described novice to start messing with. I'm all for learning DIY skills, but I get cautious when doing something wrong can start a fire or cause injury. I had your limited knowledge many years ago and ruefully remember some of the unintended mistakes I made. Do yourself a favor and get a knowledgeable friend or an electrician to help you deal with this.