Also known as TSR22a (Stop) and TSR22b(No-Stop). They refer to the observing rules. Generally they are the same except where the 5 is concerned. In both cases a foot down counts as a one. Any footing after that clicks up until you reach 3 marks lost. No more marks can be lost by footing.
To get a five, In No-Stop if the bike fails to make forward motion you get a 5 feet up or down. An engine stop is usually a five unless the bike is moving and the engine can be restarted without footing
In Stop Allowed a 5 is issued for rearward motion, (going backwards, e.g. rolling back down a slope), Engine stops while footing. In the case of an engine stop, if the rider can restart without footing no marks are lost.
In both rules you can also lose a 5 by Falling off, handlebars touching the ground, displacing a flag, (actually pulling it out so an Observer has to replace it), running outside a flag, outside your course or "crossing your line". If tape is used to mark the limits of the course you can also get a 5 by breaking that.
I'm Pretty certain that cover most Club Trial situations.
At beginner level just try to get though as best you can. If you have an ACU Trials card already you can join any club and ride their Trials. Most around here charge £15 and it between free and £10 for single membership and some clubs allow Family membership At £15. Most clubs have a Day membership fee where if you just want to see what you think you can ride that day.