上网(shàng wǎng) - to go online in Mandarin

上网 (shàng wǎng) means to go online, built from 上 (shàng, to go up onto, to get on) and 网 (wǎng, net). English pictures the internet as a place you enter; Mandarin pictures it as a surface you climb onto, the same 上 (shàng) used for boarding a bus, 上车 (shàng chē).

It is a verb-object compound, not a single fused verb, which matters for word order: time and duration go between the two halves rather than after the whole phrase. 我上了半个小时的网 (wǒ shàng le bàn gè xiǎo shí de wǎng), "I was online for half an hour", puts 了 (le) and the duration inside 上网 (shàng wǎng) rather than tacking them on the end, which is where an English-shaped sentence would want to put them.

上网 (shàng wǎng) covers using the internet generally, browsing, chatting, looking things up, whereas 网上 (wǎng shàng) reversed means "online" as a location, as in 网上购物 (wǎng shàng gòu wù), "online shopping". The two are easy to mix up because they use the same two characters in opposite order with different jobs.