So I just started playing the guitar a few days back and I noticed the sound is off. When I pluck a string indivually it makes a nice clean sound, but even if there's the slightest pressure on one string the sound will completely go and it will sound weird and tinny. Please help me! I really want to learn the guitar but I don't know what's wrong with it! And it's definitely in tune and the strings are fine too I think.
Uh, that's normal. Guitar strings are not (apart from very special situations) to be played with "the slightest pressure on one string": if you are touching the string at all, you are supposed to press it all the way down until its playing part does no longer end at your finger but rather at the fret (that's one of the small metal bars in the fingerboard) in direction from your finger to the sound hole. For a fretted string instrument, the vibrating part of any string ends at either the nut (which is where the string ends when your left hand does nothing) or a fret. Never at a finger or other part of your anatomy.
That's the rule. There are exceptions, but for now you don't need to bother with them.
It could be that the action on the guitar is set incorrectly or possibly the neck is warped. Also, the truss rod may need an adjustment. If you are fretting (pushing down all the way on a string) and it is not ringing out properly, it could mean that the string is hitting one or more frets closer to the bridge of the guitar. You may want to take it in to a local guitarsmith and make sure it is set up properly
First of all you have to press each finger firmly right before the frets but don't press harder than needed. On an acoustic guitar you have to press harder than on an electric guitar and if the action of the strings is high (distance to the fretboard) you also have to press harder.
Clip your nails because it's almost impossible to play the guitar (i.e. on the fretboard) when your nails are too long.
Very important: you'll have to grow calluses on your finger tips! You will get this by playing a lot but beware not to overdo it when you're just starting because you don't want any blisters. You will get calluses within a week or so and after that it will get thicker and harder. If you do not have calluses yet, it's very hard to get a nice tone from your guitar so please be patient. You can speed up calluses growth by never washing your hands right after or before playing and by wetting your finger tips a few times a day with rubbing alcohol (this makes them dry which is exactly what you need). There are more tricks but keeping them dry is the most important. Don't wash your hands too often!
At last there's the finer technique of placing the fingers the right way. Only use your finger tips and place each finger precisely so it won't accidentally mute the other strings. Search Youtube for guitar lessons for beginners (only watch video's that get high ratings).