When Obi-wan is fighting Vader on the Death Star, near the end he escapes back into the hallway and summons a Force projection of himself to stand against Vader in his final moments. He causes his projected body to disappear when it is ‘struck down’, then causes the cloak to disappear some time later.
Then Obi-wan escapes the Death Star while the Rebels are attacking and telepathically communes with Luke before escaping.
He then projects himself to Luke several times after this such as on Hoth and on Dagobah, which is why his visage continues to age.
Yoda does the same thing when he ‘dies’ on Dagobah.
Anakin feigns death on the second Death Star and ditches his armor on the shuttle while Luke is distracted during flight. And, you guessed it, all three Force Lads meet up on Endor and give Luke a Force projection send off before piling into Obi-wan’s ship and retiring on Canto Bight.