Consolidate means to bring together. If you consolidate student loans, you put them all together into one big loan. If you consolidate your childhood toys, you grab them all up and put them in one place. Preferably a toy box.
Consolidate comes from the Latin roots com- ("together") and solidare ("to make solid"). So, consolidate is to bring things together to make something solid, stronger, or easier to handle. A general might consolidate his troops, a librarian might consolidate his grammar books, and someone with credit-card debt might consolidate the debt from different cards onto one.