All conjunctions join clauses. Some are coordinating and some are subordinating. Subordinating conjunctions are placed before subordinate clauses. These clauses cannot stand on their own.
MC SC sentences
These sentences have a main clause, then a subordinating conjunction and then a subordinate clause.
We went to the beach when we were bored.
‘When we were bored’ is subordinating because it cannot stand on its own.
SC, MC sentences
These sentences place the subordinate clause first in the sentence.
When we were bored, we went to the beach.
A white bus
A good way to remember which conjunctions are subordinating is ‘A white bus’:
Although When However If Though Even though Because Until Since