I ran into a lndmine, but I can't figure out how to use stimpacks to heal my legs...

Open your pipboy and apply a stimpack from the status window far left tab.

Yes but can you actually target a specific limb? Or is it just the same as taking a stimpack in general?

so far i've just been using a stimpack out of the pip boy. I haven't had the abilty to target specific limbs like in previous games. Not sure if that is because im being a derp though.

Stimpacks seem to heal all limbs, but it doesn't happen immediately. Both of my arms were crippled by an explosion and I used one stimpack; they were at full health after some time again.

Yeah that's my issue... It has to be doable but I don't get it..

No you can't add to limb that needs it anymore. After you use it from the status tab on the pipboy and back out to normal gameplay you will see top right of the screen pipboy walking just fine for a few seconds instead of of crutch and bandaged leg.

On console, it seems you just need to use a stimpack(s) to heal up. You no longer need to pick specific limbs to heal, they all heal as one when you use a stimpack. On PC...I'm pretty sure my brother (who plays on PC) said he can target specific limbs for healing.