For homing bullets:
Add the bullet behaviour to your bullet. Make sure "Set Angle" is ticked on the project properties.
If you want you bullet to always target the nearest enemy, even if the nearest one changes, then do the following every tick:
System condition: For each bullet, pick nearest enemy to bullet.X, bullet.Y
Bullet action: rotate n degrees toward enemy.X, enemy.Y
The greater the value of n the more the bullet will home in.
If you have a lot of bullets and performance is suffering swap every tick for every t seconds and increase n.