One you have found a boat to hop onboard, the skipper will provide you with a list of things you will need. Don't worry if you don't have 'designer sailing gear' when you are just seeing whether sailing is your cup of tea. Garden wellies instead of sailing boots, and blankets instead of sleeping bags will do just fine.
Typically you will join ship an hour or so before departure, or else spend an evening onboard before a morning start. The latter has much to commend it, in that you can familiarise yourself with the layout of the boat, get to know the people when they are relaxed and not focusing on some immediate task in hand, and the skipper can talk you through what's in store the next day and the tasks that you can help with.
From the moment you step aboard you will be subjected to a flurry of nautical terms - new words to be used instead of every days terms that you might have used (e.g. the 'front' of the boat is referred to as 'the bow', the 'kitchen area' as the 'galley' and the 'toilet' as 'the heads'. Everyone takes a little time to learn the new jargon.
Prior to setting off the skipper will usually provide a safety briefing, which will include issuing you with a harness on providing guidance of its fitting and adjustment (safeguards your becoming separated from the ship). You will be shown places to which the harness can be attached and given guidance as to when it should be used. You will be provided or shown the location of lifejackets (inform the skipper if you are a non-swimmer).
Ideally your first sailing trip will be on a nice warm sunny day. First impressions are important - a cloudless sky, warm sunshine and smooth sea rather than an overcast rain swept day with a lumpy sea is more likely to encourage the desire for a second sailing trip !
You may be concerned about the possibility of suffering sea sickness, and wondering what you can do to minimise its likelihood:
be rested before the start of trip, avoid alcohol and spicy food
take plenty of warm clothing
choose a day sail for the first trip
you may wish to consider taking preventive medicine - though
seeking natural immunisation may e a better option as the various sea sickness
tablets may cause side effects such as drowsiness
if you are a smoker and there is a non smoking policy onboard if may help if you take some nicotine patches !
A yacht isn't a fast vessel and on a 30ft something single hulled boat, a peed of 6 knots (slightly more than 6 miles per hour) is considered a reasonable speed. Sailor's don't expect to get anywhere quickly. The travelling is a major part of the experience, and satisfaction is often derived from using the wind and tides to best advantage (rather than getting from A to B in the shortest possible time.
It may surprise you how far the boat heels (leans over) but it is normal ! In fact the boat moves in three planes - with pitching, rolling, and yawing all present to some degree. In response you'll find that your need to brace yourself against the boat's movements, with muscles being tensed and re-tensed accordingly. It soon becomes automatic - but is one factor why after completing your first trip you may feel tired having burnt up energy in this way and by your body in providing heat to keep your going in the outdoor environment.
Steering the board may be an unusual experience to start with, particularly on a tiller steered boat. In a car if you want to go right you turn the wheel right whilst on a tiller steered boat you have to push it to left (or 'port' using the correct nautical terminology!). Ordinarily the person steering is responsible for keeping look out (for other vessel and hazards in the boat's path), but on your first trip others will take care of this as you get used to steering the boat and using the comp-ass to keep to a heading.
Sailing is quite a gregarious activity. It's usual for every one to muck in to share the work load according to their skills and experience, with the latter passing on their knowledge. Generally those onboard share the costs of the trip (a share of food, diesel and mooring costs - if any).
One the boat has returned to its berth (normal place of rest in it's home port), it is customary for all onboard to share the post trip chores with the aim of leaving the boat ready for its next trip, e.g. washing up dishes, wiping work surfaces, taking rubbish ashore, topping up the fuel and water tanks, putting the sail cover on (a protective cover which prevents it being damaged by the UV in sunlight).
Have fun - see you afloat !