What does the phrase “Bob's Your Uncle” mean?
A good day to you too, Liyana Razak.
The phrase your friend used is commonly used in the United Kingdom. Someone uses it when they are giving a set of instructions or when a result is reached. A long version of this phrase is “Bob’s your uncle and Fanny’s your aunt.” It means means "and there it is", "and there you have it", or "it's done".
We can say, “You just need to press this green button and then wait for the copies to go through the other side. That’s it, Bob’s your uncle.”
Your friend might be implying that baking a cake will be a "piece of cake".