An auxiliary verb attached to a verb stem to express politeness toward the listener/reader (the -masu polite form).
毎朝、パンを食べます。
I eat bread every morning.
昨日、友達と映画を見ました。
I watched a movie with a friend yesterday.
明日、図書館へ行きますか？
Will you go to the library tomorrow?
すみません、もう一度説明してください。
Excuse me, please explain it once more.
Archaic/humble auxiliary use: in older language, used to express humility or respect toward those affected by the action.
古文では『参らせま（す）る』のように、ます系が謙譲や丁寧の一部として使われることがある。
In classical texts, forms like 'mairase-masu(ru)' show that masu-forms could be part of humble or polite constructions.