Troubleshooting:
Make sure that your fingers and hands are only pressing where the dots are represented on the chord chart. If the 2nd and 4th strings aren't making noise you probably need to press FIRMER. (it will be slightly uncomfortable. You'll get stronger, I promise. If the 1st and 3rd strings aren't making noise then check your fingers and hands and make sure you aren't accidently touching those strings.
For sound to be produced there must be vibration of the strings.
A chord is playing multiple notes at one time. There's usually 3 notes but there can be more. In the name of the chord we get a lot of information. Musicians know the difference in types of chords because of the way that they sound and also the mathematical formula and the distance between the notes in the chord. I am going to use a piano daigram to help you see the distance between notes.
This means that the chord consists of its usual notes but ADDs the 7th note away from the base of the chord. Take F7 for example. it consists of F, A, C, and E. 7 chords can be major or minor (or other things). You'll know the difference in the name of the chord (i.e. F, F7, Am, Am7.)
F is the base of the chord. if you count the white keys starting with F the E is 7 notes away.
F-1, G-2, A-3, B-4, C-5, D-6, E-7