Overheating & alternator.

I have a '93 ford explorer. I got home and all of a sudden my engine is overheating with steem everywhere. I hear a loud hissing noise where it is coming from. I added coolant just a few hours ago then drove if and it still did it again. Now the meter stays at normal but when i check the engine I still hear the loud hissing noise. What could it be? Hose, pump what???

Also, my car has problems starting. It has for a while. Sometimes goes and sometimes it won't. I think it may be the alternator. I get verry little power and the lighs are very low when it won't start. When i try and lock the doors all i hear is the locks slowly going down. Can a bad alternator cause my battery power to be low? It works when I jump it but unless I jump the car it won't start. If you can help thanx

Poor starting: Start with basics...battery, cables, clean battery posts and cable terminals.
If this 93 has an ammeter gauge on dash, when it's running, is the needle barely on the + side or on the - side? How about when it's idling?

Overheating: When it's running, look underneath, any coolant dripping? Shut it off, now any dripping?