How to vent garage in summer

Go to any big box store and get some 6" flexible insulated duct (this pic shows black sheathing on the outside, but it's often made of shiny reflective mylar):

And a couple of 6" boots, one for each end:

Use aluminum HVAC tape or a large band clamp or zip tie to connect the inner sleeve of the duct to the boots, then use another layer of tape to seal up the insulated layer and prevent it from sliding around. Cut holes in the ceiling to match the rectangular boot opening, keeping one long edge of each hole flush to a ceiling joist. Then take your duct assembly up into the attic and insert the boots into each hole. You can just leave the flexible duct lying on top of the ceiling joists. Back downstairs, use small nails (with heads, not finish nails) to nail through the inside of the boot opening into the side of the adjacent ceiling joist. Then install a couple of register grilles and you're done!

The easiest way to insulate concrete block is to glue foam insulation board directly to the block. These boards come in 4 ft X 8 ft sheets and different R values. The other method is to build a wood or steel stud wall along the block to hold blanket style insulation along with electrical wiring etc. This method is a lot more work, but gives you a base to install sheetrock later on.

Depending on whether or not you want the attic area insulated or not, blanket or blown in insulation can be installed into the ceiling. ( this assumes you have a sheathed ceiling). Otherwise, you can install blanket insulation between the rafters. Depending on budget, sprayed in foam insulation is fantastic. You may also want to look at some venting to help exhaust hot air during the summer months. I may add a few comments later, but here's a start.