Declare of Interest

What's the difference between showing interest, declaring interest and doing everything to sign someone?

There are 3 levels when you declare interest on a player, and i've never been able to understand the difference.

I think it shows how bad you want him and thus how much you're willing to do in order to get him.

I dont try to sound desperate because i think if you do the club might try up the transfer fee and make you pay more so I just show interest to try and coax the player but most of the time I do my transfer dealings privately without declaring an interest