To expand the expression $(a + b)^2$, we use the binomial theorem:

$(a + b)^2 = a^2 + 2ab + b^2$

Here's a step-by-step breakdown:

1. Square the first term: $a^2$.
2. Multiply the first and second terms, then double it: $2ab$.
3. Square the second term: $b^2$.

Therefore, $(a + b)^2 = a^2 + 2ab + b^2$.

Would you like more details or have any questions about this?

Here are some related questions you might find interesting:

1. How do you expand $(a - b)^2$?
2. What is the expansion of $(2a + 3b)^2$?
3. How do you factor $a^2 + 2ab + b^2$?
4. What is the binomial theorem?
5. How do you expand $(a + b + c)^2$?

Tip: When expanding binomials, always remember to apply the distributive property (also known as the FOIL method for binomials).