The character 加 (jiā): to add

A Chinese street stall: a wide counter of pale wood, a cream plaster wall, a small latticed window and a bamboo blind. On the counter, a tall stack of honey coloured bamboo steamers gives off white steam, and one more basket with its woven lid waits beside it. On the wall at the right, the character 加 in dark brown: a bar that runs along the top, turns down and ends in a small hook, crossed by an oblique from above, and beside it an empty upright rectangle set lower.

Pronunciation: jiā
Strokes: 5
Radical: 力
Made of: 力口

What it means

to add; plus; (used after an adverb such as 不, 大, 稍 etc, and before a disyllabic verb, to indicate that the action of the verb is applied to sth or sb previously mentioned); to apply (restrictions etc) to (sb); to give (support, consideration etc) to (sth)

Where its shape comes from

Xu Shen takes it apart without hesitating, "from 力 (lì), strength, and 口 (kǒu), the mouth", and glosses it as "words piling up on one another", which in its old sense means laying it on about somebody. The composition is not in doubt; what the two elements do together is. Strength on one side and the mouth on the other yield effort quite as readily as speech, and the reference works do not settle the matter.

Source: Xu Shen, Shuowen Jiezi (121 CE); the Chinese University of Hong Kong character database.

A way to remember it

Two characters you have already met, shoulder to shoulder: 力 on the left, 口 on the right, the box sitting lower than the top of its neighbour. Check the 力: its slanting stroke begins ABOVE the bar and crosses it, otherwise what you have written is 刀 (dāo), the knife.

This is a memory aid, not the origin of the character.

Words it appears in

参加 cān jiā · HSK 3 to participate; to take part; to join
增加 zēng jiā · HSK 4 to raise; to increase
加班 jiā bān · HSK 4 to work overtime
加油站 jiā yóu zhàn · HSK 4 gas station
加工 jiā gōng · HSK 6 to process; processing; working (of machinery)
加剧 jiā jù · HSK 6 to intensify

Writing it

See the stroke order of 加, animated stroke by stroke.