Congratulations on getting your first unicycle.
There’s a definite progression to the skills that you’ve mentioned.
Riding in a straight line comes with practice. Learn to look some distance ahead, rather than at the floor. Relax your shoulders, keep your weight on the saddle (not on the pedals) and aim for a smooth circular pedalling mothion. It will come with time.
Mounting without holding onto something is called “freemounting”. The difficulty with freemounting is not getting up there, but staying up there long enough to get your balance and start riding forwards.
Therefore, you need to be confident riding, and riding at a fairly low speed, even pausing for a moment now and again. If you can pause and restart (without dismounting) then that is part of the skills package you need to be able to learn to freemount.
Then the bit where you stay still on the same spot. This is called “idling”, or “rocking”. What you actually do is move the unicycle forwards and backwards under you, whilst you keep your body in more or less the same place. It’s a skill that takes lots of practice. You need to be confident at freemounting, and confident at riding very slowly, pausing, starting again. You need to find a smooth piece of ground, pump the tyre up hard, and then practise practise practise. Look a long way ahead at a fixed object.
The good thing is that idling leads naturally into riding backwards. the two skills are closely linked.
If you are that way inclined, look up the list of Skills Levels, which are fairly logically arranged in terms of difficulty.
For day to day riding, however, I’d suggest you set your sights to learn the skills in approximately this order:
Ride straight for a reasonable distance.
Stop and dismount neatly. (Unicycle in front.)
Double back somersault with a half pike.
OK, I lied about the last one.