“All right - let's get to work.”

You're leading a group of people that is decorating for a wedding. You discuss the plans with the group and tell each person what to do. Now it's time to break up and start doing the work, so you say:

All right - let's get to work.

all right

This is a transition that's often used in spoken English to shift between one mode of conversation and another. In the example above, the speaker switched from giving instructions to giving the signal to start working. It can also be used when you've been debating something and now want to announce your final decision.

get to work

This means to begin working. It gives the impression that there is some work that needs to be done, and you need to start on it. Of course, these same words can also mean "get to (the place where I) work".