Thanks but I think I wasn't very clear with my question...
I know what modulo is and I also know a little modular arithmetic but I have a confusion with the term 'congruent' (till now I have only heard of it in the connection of similar shapes and congruent shapes).
When I googled it, I read about the clock example (how it wraps around) and I also read that congruences have their own properties and are important in number theory. I can connect the clock thing to modulo but I have no idea how congruence comes in.