Quick answer
Я уже́ иду́.
ya uzhé idú — иду́ on foot, е́ду by transport — pick the right one
The options
иду́ or е́ду
On foot is иду́; in anything with wheels it is е́ду — including the metro and a taxi. Writing иду́ while sitting on a bus is the classic learner slip, and Russians notice it instantly.
Time phrases
Че́рез + accusative for “in”: че́рез пять мину́т, че́рез час. Уже́ (already) softens a late message: Я уже́ выхожу́ — I’m leaving right now.
What you hear back
Typical mistakes
Я иду́ — from the bus
Я е́ду
Transport takes е́хать.
Я бу́ду в де́сять мину́т.
Я бу́ду че́рез де́сять мину́т.
че́рез + accusative for “in ten minutes”.
Check yourself
You are on the metro. What do you write?