Hi jx210, it's really hard when you start. It's difficult if you are real beginner and your ears aren't used to recognising the pitch of notes. If you don't have a teacher who would help you with this, I would suggest that tomorrow you buy an electronic tuner. They give you a visual read-out of whether you are sharp or flat, and by how much. It really will help until you get used to using your ears more.
The main thing is, even though its frustrating, don't get dis-heartened and then give up. Problems can be solved, and you will be amazed how much pleasure you will get soon from even the smallest amount of progress.
One of your best strokes of luck, is finding us here! You will get loads of help and support. Any problems you are having, just ask.
If you need to do something until you can get your guitar in tune, why not have a read at this thread
here

One good thing about music is that when it hits you, you feel no pain - Bob Marley