If you could touch the alien sand and hear the cries of strange birds and watch them wheel in another sky, would that satisfy you?
This is a good source: https://mtg.gamepedia.com/Planeswalker
Planeswalkers enter the battlefield with a set number of loyalty counters, printed in the lower right of the card. A planeswalker can be attacked, like a player, or be dealt damage by an opponent redirecting the damage one of his or her spells would deal to the player controlling the planeswalker. Damage dealt to a planeswalker removes that many loyalty counters and a Planeswalker with no loyalty counters is put into the graveyard.
Planeswalkers usually have three abilities: one ability that adds loyalty counters as a cost for a small benefit, one that removes a small amount of counters as a cost for a larger effect, and one that removes a large number of loyalty counters for a big effect. The last effect is commonly referred to as the Planeswalker's Ultimate ability and usually leaves the opponent in a devastated state. The starting loyalty of a Planeswalker is commonly significantly lower than the cost of the Ultimate and a player has to build up the loyalty to access the Ultimate.