Don't be shy, we won't kill you.
In regards to replacing strings, you might want to replace the whole set because they might be pretty corroded, and as a result, they probably sound pretty dead. Changing strings is pretty easy.
1. Buy a new set of strings. For beginners, start with a light gauge, preferably .10s. They don't hurt to much to play. I've been playing for more than 1.5 years and still have problems with .12s on acoustic. Doesn't really matter what brand it is, Martins, D'Addarios, Dean Markleys all good.
2. Take the old strings off the guitar. You do this by loosening the tension with the tuning keys until it's loose enough to remove it from the tuning head. Then pull out the bridge pin holding that string in, and remove the string.
3. Place the end of the string with the ball/ring thingy on it into the body of the guitar, and press the bridge pin back in. Then thread the other end of the string through the hole in the tuning head.
4. Hold the bridge pin in with one hand while you tighten up the string with the tuning key. Keep the guitar facing away from you as best as possible, and increase the tension slowly.
5. Cut off the loose end of the string once it has been tuned up to it's proper pitch with a good pair of scissors or wire cutters.
That's about it. Make sure you only do one string at a time- the main reason is that it's a bad idea to leave an acoustic guitar unstrung for any length of time.
As to learning any songs, it will take a while. Learn basic chords first, and then try to find a song with simple chords in them. It take practice, plain and simple.
Andrew
P.S.: You'll need to have either a tuner, piano, or tuning fork as well to make sure you're tuning the strings properly. There's plenty of info on how to use these online- just use Google.