That one bar.....

It's called chi. You will need it for certain skills ^^
Since you're a psy I'll take a psy skill as example. At lvl 49 there's a skill called Disturb Soul.

Range 20.4 meters
Mana 112
Channel 1.6 seconds
Cast 1.2 seconds
Cooldown 30.0 seconds
Weapon Soulsphere

Requisite Cultivation Aware of Coalescence
Increases the Channel time of target by 53%
Lasts for 12 seconds.

Costs 30 Chi

As you can see it says that it costs 30 chi. So it will take 30 out of the yellow bar.

After lvl 29 you will also see a raindrop shaped pink bubble next to the bar(it will eventually become 3 of those bubbles). Those are sparks Once your chi bar fills up completely 1 will light up and the bar will fill itself up again, 100 chi = 1 spark. You use them for the skills at lvl 59 and for the skill spark eruption. This will let you dish out some extra damage for a short period of time ^^

Hope that helped

Chi is a very important thing for us psycs.
At a higher level you will be using skills constantly that require chi.
Such as psyc will, earth vector, etc. ;3