Start
Beginning, Opening
noun, verbal noun
The open of the start is the start or beginning.
Note that 開始 is slightly more formal than 始める.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
イベントの開始時間は何時ですか？
What time does the event start?
明日から新しいプロジェクトが開始します。
A new project will start tomorrow.
ミーティングの開始がおくれるって、社長にはもう言った？
Did you tell the president that the start time for the meeting will be delayed?