Will I fail driving test if I do/don't use bus lane?

I always have problems with bus lanes for some reason I always miss the sign or am confused whether or not I can or can't use the bus lane on the times on the sign and the instructor has to tell me if I can use it or not, will I fail my test if don't see the sign and use the bus lane when I'm not supposed to and will I be fined or if I don't use the bus lane when I am supposed to? Will this be a fail, minor or major mistake?

I always have problems with bus lanes for some reason I always miss the sign or am confused whether or not I can or can't use the bus lane on the times on the sign and the instructor has to tell me if I can use it or not, will I fail my test if don't see the sign and use the bus lane when I'm not supposed to and will I be fined or if I don't use the bus lane when I am supposed to? Will this be a fail, minor or major mistake?

If you drive in a bus lane which is in operation, your examiner will quickly act to tell you to move out of it. This is to avoid you receiving a fine. But yes, you will definitely not pass the test if you do this.
When a bus lane is not in operation, then you should use it. If you don't, you will at least earn a driving fault, but where you are holding up following drivers, or someone passes on your left, a serious fault will be marked and you will fail.
See here for more info - Bus Lanes
As already suggested however, why have you not asked your driving instructor this question?

"or someone passes on your left, a serious fault will be marked and you will fail"
Oh, I didn't know that.
If I remember right if your driving causes pretty much any other vehicle to have to take action it's a fail, does that also apply to undertaking? Even though they're obv choosing to undertake do they consider the learner at fault for provoking it?