how do i get mana

[oven]

how do i get mana back

[vamirez]

Drink a blue flask (cerulean tears). You can manage the amount of red and blue flasks at the sites of grace (it's one of the menu options there).

[Dark Angel]

Some talismans and weapons can also help to get mana back. One example is the Sacrificial Axe, you can get it in Weeping Peninsula when you kill a Death Bird at night there. Wield this axe or put it offhand on your back, and you'll gain a small amount of FP with every enemy kill, very helpful in large dungeons or big areas with lot of mobs.
In the open world look out for blue glowing tear scarabs, when you kill them they'll refill some blue flasks.

[Sabaithal]

Also the Ancestral horn talisman gives you back some FP on any kill. The blue knife talisman gives you some FP upon any crit.

Sacrificial Axe can be obtained early on by snipping the Death Bird from atop the ruins with a bow or something (quite an investment on arrows though).