Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Summoner spells: exhaust & flash; good offensive and defensive spells. great to ulti with or to gtfo.
items: core items, if game is long lasting get Zhonya's ring. if your farming well try squeezing Exilir of Brilliance for a quick advantage (make use of it, lasts only 4 minutes)
game start: start off with meki pendant + 2 health pots, work your pendant into chalice by the time your lvl6 you should be able to finish chalice and boots and now you can rush GA asap. late game you can sell chalice and get extra zhonya's or a SS if your struggling try banshee's.
gameplay: Galio is a beast solo laner, always try to get mid lane. last hit for extra gold and use Resolute Smite + Righteous Gust combo to farm