If you look back through some of the previous posts on this message board this year you will find that this basic question has already been asked [and answered] several times before.

However, if you're short of time, I would recommend any one, or all, of the following standard texts that are held by people interested in Heraldry.

'A Complete Guide to Heraldry', by A. C. Fox-Davies revised and edited by J. P. Brooke-Little
'Boutell's Heraldry', again revised and edited by J. P. Brooke-Little
'The Oxford Guide to Heraldry'

To this list I would now add:

'The Complete Guide to Heraldry' by Stephen Slater