How do i increase stamina?

[MAlipioC]

??

[Vilsike]

More points into Endurance

[Bored Peon]

.....

You mean Action Points.
There is no stamina in Fallout.
Your agility points is how many AP you have and the refresh rate.

Points in endurance only helps reduce the AP drain of sprinting.

[Bishop]

Its based on agility mostly. You can stack something like 40 agility easily with unyielding set of armor, some mutations and underarmor. Then there's items, food and perks that increase AP regen and legendary effects that decrease its consumption.

I'm sitting on something like 400ap right now and with grim reaper sprint it's almost impossible to run out.