Hold your guitar correctly. When you are sitting down, there are two main ways to hold your guitar. For a casual playing style, lay the guitar over your dominant leg. On the other hand, the classical method has you set your guitar on your non-dominant leg. In both instances, make sure that the guitar is held close against your body. Holding your guitar properly makes it easier to play and prevents you from becoming fatigued. Play around with both styles and figure out which one is most comfortable for you.
You’ll also notice that each button requires a different amount of pressure in order for the chord to play properly. The further away the buttons are from the guitar’s nut, the less pressure is required. Vice-versa, the closer you get to the nut, the more pressure is required (i.e. blue button requires the least amount of pressure while the yellow button requires the most).
As a beginner, it is best to avoid making a pawn shop, flea market, or yard sale purchase unless you are shopping with somebody who has experience in purchasing a guitar. Having never purchased a guitar, you may not know what to look for in terms of damage or guitar quality. With that being said, a local music retail shop is your best bet. You may also shop online with a reputable company, although be sure to review the business’ return policy.