The particle し is used to connect two or more clauses, meaning 'and' or 'and what's more'. It often implies that there are other reasons or points not mentioned. For example, you might say 'この店は安いし、おいしい' to say 'This shop is cheap, and also delicious', with the nuance that there are other good points too.

You attach し to the plain form of a verb or adjective. For nouns and な-adjectives, you add だ before し, like '学生だし' (since I'm a student). The tense is shown in the plain form: past tense uses たし, e.g., '行ったし' (I went, and...). It's common in both speaking and writing, but in casual speech you often hear it after a single clause to add a reason, like '疲れたし、もう寝る' (I'm tired, so I'm going to bed).