Could you not sit on the important documents?
Koichi and Viet are always playing whoopee cushion pranks, so I'm always careful when I sit down on my office chair.
When I’m sitting for a long time my butt gets sweaty.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means sit so the verb vocab version is to sit.
The reading is unlike the kanji reading, so let's use a separate mnemonic to remember this. Just imagine yourself going to sit down. You sit down, and the ground collapses below you and you fall. When you land, you find yourself in a nasty, stinking sewer (すわ). It is so gross. Taste the sewage in your mouth. Smell it. Feel gross. You shouldn't have sat down on that spot, it was looking awfully dangerous, now that you think about it.