Press F to access psi and your other abilities.
Also, you can click the icon that sits between your hotbar on the left and your 2 weapon slots on the right. Click that 'thing' between them (called the Quick Invoker on its tooltip).
(Then you can drag those abilities to your hotbar (incl holding down SHIFT or CTRL for the alternate hotbars)
In case Martek's answer wasn't enough...
First, you have to acquire the abilities. This is done by being trained by someone already proficient in the skill tree and you paying them/doing a job for them and receiving skills as payment. Then it will appear in your skill-menu to be added to your hotbar.
The 3 teachers in SGS are
Bisson (psychokinesis) - you have to pay him no matter what.
Ezra (thought control) - who you can get the neural overload skill from for free if your WILL is high enough (which it should be if you're using PSI abilities) - this is the 1st psi skill in the game.
Quinton (metathermics) - if your mercantile skill is high enough you can get 2 free skills from Quinton. I recommend getting 2 of the more expensive skills and paying for the first 50credit skill out of pocket.
There are more trainers and ways to learn more skills as the game goes on.
Note that you can learn 1 skill from each of these trainers without having any SP in the related tree (0SP required.) Neural overload, telekinetic punch, and cryokinesis.
I only have skill in metathermics, but I find having neural overload and telekinetic punch from the other trees useful (and no point in not having them considering the 1 is free and the other is cheap.) Neural overload for mobs that are pretty much dead so I don't waste ammo, telekinetic punch for exploding barrels.
I highly recommend planning your character a bit before getting far into the game. Check out the wiki
(it's practically the manual) for all the skill, ability, etc., information you might want.
When I first started playing, I was like "yeah! thought control and psychokinesis! COOL!", and made them my skills while leaving metathermics behind. Then I actually read what abilities are available in the skill trees, and changed everything.
This is an incredibly stupid question, but I am not ashamed to admit that I am a complete idiot and cannot figure this out. How do you use psionic abilities? How do you access them?
replying so you get notifying