170 deck belt algustment

So today I mowed for the first time with the 170 I cut for about 2 hours cut the blades off and when I cut them back on I made a squealing sound so I got off and look at the belts and the belt going from the engine to the back pulley was loose so how do you adjust this there is a little handle on the side of the deck dose this adjust it one more thing now when I try to start it it makes a click but after I do it a few times it turns over. Fine the battery is new