Awaken appears on certain instants and sorceries with two costs: a normal cost and a higher Awaken cost. If you pay the Awaken cost, the spell's normal effect happens and you put the listed number of +1/+1 counters on a target land you control, turning it into a 0/0 Elemental creature that's still a land. The land becomes a creature that can attack and block, while keeping its ability to tap for mana.
The common mistake: people forget the awakened land is now a creature and vulnerable to summoning sickness, board wipes, and creature removal—losing your mana source. It also still counts as a land, so it can be hit by land destruction too.
In Commander, Awaken offers flexibility: cast cheap early, or late-game pay the Awaken cost to get a free, sizable body alongside the spell's effect, making cards like Scatter to the Winds efficient two-for-ones.