If you know how to play an E major chord, then you know how to play an A minor chord—just move the chord whole shape over a string. Make sure your first finger is curled, so the open first string rings clearly. Avoid playing the open sixth string when strumming the A minor chord. There are situations when it makes sense to reverse your second and third fingers when playing the A minor chord.
You can tell whether or not strings are of a thin or thick gauge based on the numbers on the package. The smallest number, which is the gauge of thinnest string, will usually be .9 or lower on thin gauge strings. On thick gauge strings this number will be .12 or higher. Strings that are .10 or .11 are generally considered to be “mediums”, and produce a tone and feel which is the middle ground between these two extremes.
The Guitar Program at Musicians Institute is designed to develop professional level technique and musicianship through performance-intensive and immersive experiences. Guitar classes are taught by leading professionals and students will get trained in the basics of guitar playing, including performance, ear training, melodic soloing along a huge variety of contemporary styles.