A clause is a series of words that contains a subject doing an “action” (in the form of a verb).
“Since she likes me”
“I like her”
“Because she didn’t reply”
“I called my mom”
If the clause can stand by itself and form a complete sentence, then it is an independent clause.
“I like her” and “I called my mom” are examples of independent clauses.
If instead a clause has a subject “doing” a verb, but is preceded by a conjunction, then it is called a dependent clause. Dependent clauses cannot stand alone, and must be connected to an independent clause to form a complete sentence.
“Since she likes me” and “Because she didn’t reply” are examples of secondary or dependent clauses.
Dependent and independent clauses can be combined to form sentences (not to be confused with phrases)
“I called my mom because I wanted to talk to her”
“I called my mom…” = Independent clause
“…because I wanted to talk to her” = Dependent clause