What's the difference between getting my expanders tightened and my actually braces? (photos)

i have expanders with my braces and and my orthodontist has been tightening it for the past 2 months but my mom told me that I won't have the expanders for the whole two years that they are just to help my teeth have space ! My question is I'm confused with the whole expanders and getting my actually graves tightened what's the difference??

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