Cepheids
This is a group of stars that dim and brighten periodically. They can then measure its brightness which tells astronomers how far away it is.

Supernovae
Astronomers use this method when determining distances in very far away galaxies. They know how far away one star is and how bright the star is, so they compare it to the unknown object to determine the distance.

Redshift
This method created by Edwin Hubble is for very far away objects that cannot be measured by other methods and is based on the idea of expansion. If the lines are shown shifted towards the red side it means the object is moving away and is moving towards us if it is towards the blue side. It can also show you how far away it is based on how far apart the lines are.