What phone, what android version, and do you mean pictures from the camera, or downloaded from the internet, or...?
Assuming it is the camera then the first thing to try is opening the camera app's settings and looking for an option to specify the location it stores images to. (Edit: ah, I see girolez beat me to that!).
To move pictures manually you'll probably need a "file explorer" app, unless the gallery app can do it. If I seem uncertain it's because many manufactuers include their own camera apps and gallery apps, so they will be different on different phones. Some phones come with a built-in file explorer, some don't. That last point may matter if the phone is running Android 4.4, since Google were a bit over-enthusiastic about SD card security in that release and 3rd party apps (those you install yourself) may not be able to write to the SD card.