Conjunctions are used to link two similar grammatical structures. For example, and links two nouns (my brother and my sister), while that links two verb phrases (She said that you are leaving).
Here is a list of English conjuctions: and, if, that, but, or, nor, so, yet.
Here are some points to keep in mind when writing with conjunctions:
a) use a comma before and when it joins two independant clauses, e.g.: I work at night, and she works during the day; don't use a comma before and if it joins two verbs or nouns (e.g.: I play and sing; I like tofu and rice).
b) use a comma before but.