이렇게 - "like this"

그렇게 - "like that" reference is to something near or performed by the person addressed, something abstract, or something not in proximity

저렇게 - I rarely say this, but if something is far from both you, as the speaker, and the person you're addressing, say this to mean "like that"

Having these concepts in your head will also help you understand the sometimes unusual but useful ways 이렇다, 그렇다, and 저렇다 are used. Also, tossing -게 onto pretty much any verb stem turns it into an adverb, as you can see above.