"In the name of God, the Most Gracious, the Most Merciful"
Its a powerful phrase that completes our actions and adds immense reward and barakah to everything that follows it.
It literally means that we start our action seeking help and blessings through the same name of Allah. Essentially, when we say bismillah we remind ourselves that everything is for Allah alone. Our sustenance, future, akhira lie with Allah alone.