How to Use an Expression to Assign a Value Into a Variable

Ifs are more explicit and easier to read, but they can't be used as an expression. So do expressions change that? You do let's say let X equals do open curly brackets. And from that point on, until the end of the curly brackets, everything in it behaves differently. It's kind of like doing using an iffy, a self-invoked anonymous function where you want to assign some value into a variable.