verb · to learn the basics of a subject; a primer or introduction to a field

如果你想学习围棋，这本书是很好的入门教材。

verb · to enter a door or a house; the entrance door

他一入门就闻到了厨房传来的香味。

adjective · (attributive) designed for beginners; the basic or introductory model of a product line

对于摄影爱好者来说，这款入门级相机性能很均衡。