This video will teach you the basics about time signatures. Fiddlerman will show you the most common time signatures along with a few basic note lengths plus a basic explanation of tempo markings and what they mean.
Learning to play an instrument visually with music greatly eases the effort of learning to read music later. Basic knowledge of music theory is easy to learn step by step in conjunction with learning the instrument. If this video confuses you the first time just repeat it a few times until you catch on.
Top number on a time signature represents the amount of beats in a measure while the lower number shows us the note value which will be receiving one beat.