Car Remote
 

I bought a used Honda Pilot 2015. The car didn't come with a remote to lock/unlock the car. It only came with a key.

How do I get a remote for this particular car?

Buy and install or take it to a place that can do it.

Can I buy the remote itself? I don't know what I am looking for. Part #?

Does the ignition need to get rekeyed in order for me to get a new key and remote?

Have you even tried. Quick search.
https://www.google.com/search?client...15+honda+pilot

When you lock and unlock your car, do you use a remote (transmitter) or do you put a key into the door and unlock it the manually way?

Your questions can be answered by reading what the kit can do. You'll find one that can do what you want.