Learn Italian: Ho mangiato una pizza intera da solo.

Yes, it is a related concept! While you are learning words like la metà (half) and un terzo (a third), intero means "whole" or "entire." Because it acts as an adjective here, its ending changes to match the noun it describes. It takes the feminine singular ending to match pizza.

Why use da solo instead of just solo?

Solo by itself often means "only" or simply "alone." However, the specific phrase da solo means "by oneself" or "on one's own" (meaning without help or company). In this sentence, it translates to "by myself."

If a woman is saying this sentence, does she need to change da solo?

Yes! The word solo in the phrase da solo must agree with the gender and number of the person it refers to. A man says da solo, but a woman would say da sola. If a group of people did something by themselves, they would use da soli or da sole.

Could I put intera before the noun, like un'intera pizza?

You can, but placing the adjective after the noun (una pizza intera) puts a stronger emphasis on it. By putting it after the noun, you are really stressing the fact that you ate the whole thing, which sounds very natural for this kind of boast or confession!