Help what is a sub clause .

[overweightnoverdrawn]

I havnt a clue Ds is in yr 5 aged 9 .

does this help?

Isn't it a part of a sentence which could be omitted and it still make sense ie.

The red car, which was going too fast, overtook ours and had to brake hard.

sub clause = subordinate clause

As she ran, her heart pounded.
Her heart pounded as she ran.

The main clause is "her heart pounded" - this could be a sentence in its own right with a capital letter and a full stop.
The subordinate clause is "as she ran". This doesn't make sense on its own, and depends on the main clause for its meaning.

does that help?