At 70% or greater equipment load, you will "fat roll", a much slower rolling animation in which you are largely vulnerable. Your roll speed (and the number of frames for which you are invincible) relies on your equipment load. When you execute a roll, you are temporarily immune from damage. If you die again before you can reach the spot, the older blood stain will disappear. Return to the place where you died, and you'll be able to recover them. The souls you drop will turn into a blood stain (green) and remain in the area you died in. When you die, you'll drop all of your possessed souls on the spot.
When you die, all the souls you possess will remain on the spot, and you'll return to the last bonfire you rested at. Resting at a bonfire resurrects most enemies you have killed since your last rest, certain enimes will not respawn. Bonfires also replenish your Estus Flask uses bonfires also cure all status effects. Rest at one of the many bonfires found in the world to restore your health and FP (focus points). Press the □ (PS4) or X (Xbox controller) button to use the currently equipped item. Press the R1/R2 buttons to perform a light/heavy attack or the L1 button to guard (if a shield is equipped on your left hand). Press X (PS4), A (Xbox controller) or E (PC) to perform the corresponding action. When you approach something you can examine, open, or pick up, you'll see an onscreen message. Push the left stick a little to walk, or all the way to run.
(See the controls page for full control configuration.)