The "3 actions per turn" usually refers to the three actions you can do: an offensive, defensive and support action in one post. Though there are some exceptions to this, and performing certain techniques usually takes up an action in two separate posts. Which includes, but is not limited to the following.
Susanoo - one action per advancing form. In other words, you can form the skeletal on your first post with it, complete with the second, full with the third and perfect on the fourth. (Note: Perfect usually refers to just an additional/more composed form of Susanoo, instead of the gargantuan behemoth that Madara was shown to use. But even then, using it at all is still debated upon.)
Sage Mode - If you have Perfect Sage Mode (six resets into it) then you only need one action in gathering enough natural energy to go Sage Mode in your next posting. (I've been seeing this get skipped quite a bit recently.) Anything lower (3-5 resets) usually takes longer.
But when it comes to clones and summons, it can get really iffy and messy. I would like to ask, do clones and summons count as separate entities and get their own three actions, or do their actions count for the poster's actions as well? And what about the number of actions a person is allowed when dealing with multiple attacks on them alone?