Search your library for a Plains, Island, Swamp, or Mountain card, put it onto the battlefield tapped, then shuffle.
Farseek is one of the best two-mana ramp spells in green, and its strength comes entirely from a single word: it can fetch any basic-type land, not just basics. That means it grabs dual lands like shocklands (Steam Vents, Stomping Ground), Triomes, and other typed lands — fixing your colors and ramping at the same time.
This is why Farseek shines in multicolor decks. If your commander has three or more colors, you're almost certainly running typed duals, and Farseek effectively tutors mana-fixing while accelerating you to a turn-4 commander. It's a staple in Sultai, Temur, and any midrange/value pile that wants smooth mana.
The catch:Farseek can't grab Forest. In a mono-green or Forest-heavy deck with no non-Forest typed lands, it does literally nothing — play Rampant Growth or Nature's Lore (which fetches Forests) instead.
Bottom line: if your manabase has shocks or Triomes, run it. If it doesn't, skip it.
Farseek can find any land with any of the listed land types, including nonbasic ones, even if that land is a Forest in addition to one or more of those types.