to greet someone or call out to them; to start a conversation by addressing someone aloud.
通りすがりの人に声をかけて道を聞いた。
I called out to a passerby and asked for directions.
授業の前に先生が廊下で生徒に声をかけた。
Before class the teacher greeted students in the corridor.
知らない人に突然声をかけるのは失礼だ。
It's rude to suddenly call out to a stranger.
to invite someone, get in touch with them, or let them know (you are available); to contact someone to arrange or invite.
今度の飲み会に声をかけてもいいですか？
May I invite you to the upcoming drinking party?
後で仕事のことで声をかけますね。
I'll get in touch with you later about the work.
イベントのスタッフに声をかけて人手を集めた。
We asked event staff to recruit people.
to cheer on or give vocal support to someone (e.g., at a sporting event); to encourage by calling out.
試合中、観客は選手に声をかけて応援した。
During the match the spectators cheered on the players.
最後の一周で友達に声をかけて励ました。
On the final lap I called out to my friend to encourage them.