I'll just sumarize here some important topics!
As you can see, Q# uses C#-like semicolons and braces to indicate program structure.
Q# has an if statement that is very much like C#.
Q# deals with variables in a unique way. By default, variables in Q# are immutable; their value may not be changed after they are bound. The let keyword is used to indicate the binding of an immutable variable. Operation arguments are always immutable.
If you need a variable whose value can change, such as numOnes in the example, you can declare the variable with the mutable keyword. A mutable variable's value may be changed using a set statement.
In both cases, the type of a variable is inferred by the compiler. Q# doesn't require any type annotations for variables.
The using statement is also special to Q#. It is used to allocate an array of qubits for use in a block of code. In Q#, all qubits are dynamically allocated and released, rather than being fixed resources that are there for the entire lifetime of a complex algorithm. A using statement allocates a set of qubits at the start and releases those qubits at the end of the block. There is an analogous borrowing statement that is used to allocate potentially dirty ancilla qubits.
A for loop in Q# always iterates through a range. There is no Q# equivalent to a traditional C-style computer for statement. A range may be specified by the first and last integers in the range, as in the example: 1..10 is the range 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. If a step other than +1 is needed, then three integers with .. between them is used: 1..2..10 is the range 1, 3, 5, 7, and 9. Note that ranges are inclusive at both ends.
The BellTest operation returns two values as a tuple. The operation's return type is (Int, Int), and the return statement has an explicit tuple containing two integer variables. Q# uses tuples as a way to pass multiple values, rather than using structures or records.