し (Reasons)

Like て, し is a conjunction particle. This means that it is used for linking the (A) and (B) parts of a sentence, and describing that link in some way. The 'description' that し will highlight is 'reasons'. Regularly it is translated simply as 'and'.
し may be connected to the end of almost any word, but will require a だ before it when it comes after nouns or な-Adjectives. し will follow every 'reason' that is being listed in a sentence. However, the last し may be replaced with から or ので, before the 'result' is stated.

• 彼女(かのじょ)はピアノが弾(ひ)けるし、スポーツができるし、彼女(かのじょ)に出来(でき)ないことはないと思(おも)う。
  She can play the piano and she can do sports. I think there isn't anything she can't do.
• このレストランは高(たか)いし、まずいし、何(なに)もいいところがない。
  This restaurant is expensive and doesn't taste good. There are no good parts.
• 彼(かれ)は真面目(まじめ)だし、親切(しんせつ)だし、彼(かれ)と友達(ともだち)でよかった。
  He is serious and nice. I am glad that he is my friend.
• 今日(きょう)は休(やす)みだし、晴(は)れだし、今日(きょう)は公園(こうえん)に行(い)こう。
  Today is my day off, and it's sunny, so let's go to the park.

Using し will indicate that each 'reason' being listed is of equal weight/importance. Because of this, it would not be appropriate to use in sentences where one of the reasons clearly far outweighs everything else.

• 昨日(きのう)は雨(あめ)が降(ふ)ってたし、おばあちゃんも亡(な)くなったし、悲(かな)しいな。
  It was raining yesterday and my grandmother also passed away, so I'm sad. (Unnatural Japanese, as the level of sadness between losing your grandmother, and it being a rainy day would be completely different)