How do I give the dog a stimpack?

If your companion is out of the fight - in Dogmeat's case, if his back legs have collapsed and he's whimpering in pain - you will have the option to administer a stimpack and revive them. Note that this merely hastens their recovery - they will fully recover on their own, given time.

You can't administer a stimpack if they're still up and about.

I don't think they recover til you're out of combat if you don't give them a stimpak

Giving companions a stimpak is kinda pointless, since (as previously mentioned) they'll heal on their own after combat anyway.

That said, I personally like to give them one sometimes, as my way of showing them that I care enough to help them heal when they need it.

But as for the question, if you get close enough to the dog while you are still in combat, you should see the option to give him a shot. After that, it simply a matter of hitting the proper button to do so.

i've revived dogmeat in battle multiple times ...after i killed the enemies near him, i advance and revive him so he can keep helpin me take out more enemies advancing towards us

This is correct.

I've had the dumb dog whimpering in front of a machine gun turret before for about 5 minutes, while I cleaned up everyone else..what he gets for jumping in front of the damn thing..

With a knicknack paddywhack.

just want to throw in here that since i've learned a lil more about the dog's mechanics and started to command him more, he's becoming a lot more useful

being more proactive in controlling your companion instead of relying on them to be perfect mind readers will result in a more pleasant experience

i believe this is the whole purpose to a companion, someone who willingly follows you and will do whatever you tell them (just remember you have to actually TELL them xD)

i did have one problem tho, when i was in sewers in Concord, i came across a Mirelurk; i sent dogmeat to go 'investigate' (why not attack?) the mirelurk and he just went right up to it...nothing happened...and then he comes back; now i dont know if its cuz they're both animals that they dont aggro or what, but it wouldn't give me the option to tell dogmeat to 'attack' it and the mirelurk didn't aggro until i got close to it....

perhaps i didn't do something right with the commands...? but this did irritate me a lil, i should be able to tell the dog to attack the mirelurk without having to aggro it first