See our Hebrew alphabet pronunciation guide
Tu Bishvat is often misspelled as Tu B'Shvat in English. The word Sh'vat has a "shva" under the shin. The bet prefix (meaning "in") also has a shva. Hebrew does not allow for 2 consecutive shvas at the beginning of a word so the first one under the bet becomes a chirik, roughly equivalent to the English short "i" sound.