入门

entrance door / to enter a door / introduction (to a subject) / to learn the basics of a subject

to enter / to go into / to join / to become a member of / to confirm or agree with / abbr. for 入聲|入声[ru4 sheng1]

gate / door / CL:扇[shan4] / gateway / doorway / CL:個|个[ge4] / opening / valve / switch / way to do something / knack / family / house / (religious) sect / school (of thought) / class / category / phylum or division (taxonomy) / classifier for large guns / classifier for lessons, subjects, branches of technology / (suffix) -gate (i.e. scandal; derived from Watergate)

introductory course / primer

entrance and exit door