One of the first things you should learn in learning to play the guitar is tuning your guitar. No body like to hear a song when it is out of tune. You should know what the note is for each guitar string
Then you should get yourself an electronic tuner.
It is a good little investment for learning guitar and it will make your life so much easier. It is a little device which is operated by batteries. It can pick up the sound when you play the guitar string and it will indicate if the string is in tune or not. The tuner can pick up sounds from a built in microphone or it can be plugged into your electric guitar or acoustic guitar
They can cost from $10 to $50, some will cost up to $500. I suggest getting something around $20 to $30. So the quality is acceptable and it will last you for years. I personally use an effect pedal with a built in tuner. If you are really serious about playing guitar and would like to have a bit more fun, it is also good to get an effect pedal with a built in tuner so you don’t have to buy two separate devices. But if you like to take your guitar to different places and don’t want to carry too much cables and stuff, a stand alone electronic tuner would be convenient to carry in your pocket or in your guitar case.