בָּרוּךְ אַתָּה ה׳ אֱלֹקֵינוּ מֶלֶךְ הָעוֹלָם, בּוֹרֵא פְּרִי הָאֲדָמָה
Baruch atah Hashem, Elokeinu melech ha'olam, borei pri ha'adamah.
Blessed are You, Hashem our God, King of the universe, who creates the fruit of the ground.
Vegetables, legumes, and fruit that grows from the ground or on a plant that is not a tree get Borei Pri Ha'adamah.
In halacha the banana grows on a plant that is not a tree, so its bracha is Borei Pri Ha'adamah.
After eating: Borei Nefashot, after eating a kezayit or drinking a revi'it.
This follows the common ruling of most poskim. For different customs or a specific question, ask a rabbi.