New to Cycling today!
 

A co-worker gave me a 2016 specialized today as well as a smart trainer. I plan to mostly use this indoors on the trainer and would like to replace the platform pedals with clip-in.

Anyways. It looks like the Shimano SPD are easy to come by secondhand. My question is are the cleats and the pedals sold separate. How can I assure a shoe will fit my new pedal? I may just be tired this Monday morning, but the pedal thing is confusing the hell out of me. Also will the pedal connect to the crank(?) a universal size or do I need to worry about that as well.
I'd rather not buy new from a shop but I realize they would be the easiest route. If possible Id like to buy secondhand.

Thank You!

Cleats usually come with the pedals when you buy them. I assume when you say "SPD" you mean the type below? The shoes are SPD compatible if they have the two oval-shaped slots. There's another newer type of SPD pedals, but they are less common.

http://i.ebayimg.com/images/i/151329...-1/s-l1000.jpg

What kind of bike is it?

Shimano is a bit confusing with their cleat system. There is the SPD as shown above which is intended for mountain bike use. Some people use them on road bikes as well. My wife uses something similar on our tandem. Then there is the SPD-SL which is for road use.
For a road bike, I prefer the Shimano SPD-SL.
For my mountain bike, I use Crank Brothers Egg Beaters with something similar to the SPD.
There are a lot of options out there.

Generally speaking all pedals should fit the cranks on your bike/trainer.

Its really not too expensive to buy a new set of pedals for $50-$75 and you’ll really want to head to a shop and try on some shoes first hand. I went with Shimano RP3 shoes since they had configurations for both SPD and the three bolt cleats. This way I could try multiple pedals to see which I liked better for my road bike (ultimately went with the Look Keos).

Thanks, I really was expecting a much bigger price tag. I think Ill try the shop now. I appreciate everyones help.