The Kingdom of Loathing is a turn-based game. Turns are called adventures. One adventure is long enough to go looking for something to do/kill in a location, to cook yourself some food, mix yourself a drink, or smith yourself something. Things that cost adventures are marked with the number of turns they take, like so: (1). Vacationing at The Shore, Inc. as well as jewelrymaking (and Really Expensive Jewelrycrafting) take (3) adventures. Adventuring underwater usually requires (2) Adventures, but under certain conditions will only take (1).
Some activities, such as purchasing a trophy, visiting a store, or talking to the Deep Fat Friars do not cost adventures, but they usually don't earn you items, stats or Meat. Most non-adventure actions can be found in the Seaside Town. Such links will not have a (1) after them. If you have a bartender-in-the-box or chef-in-the-box, you can mix fancy drinks or cook fancy dishes without using adventures. Muscle signs can smith some items by visiting Innabox to avoid using an adventure smithing.
Choice adventures that include a cancel option (notably the Wheel in the Clouds in the Sky, Keep On Turning adventure in The Castle in the Sky) will usually not cost you an adventure to cancel. In the Daily Dungeon, having a skeleton key allows you to get past a locked door without using an adventure.
You can get more adventures during the day by eating food, drinking booze, and using spleen items. Besides those common ways to gain adventures, there are a few more obscure ways. Some chocolate items will give adventures. Once a day using essential tofu or software glitch will each grant adventures. The no-longer obtainable (and never tradable) Time Juice gives one adventure per juice. Some familiars and items can spontaneously grant adventures while you adventure with them: Temporal Riftlet, Mad Hatrack with a time helmet, Reagnimated Gnome with gnomish housemaid's kgnee, and V for Vivala mask. Once per ascension, choosing to head towards the top of The Hidden Temple grants 3 extra adventures.
Each day at rollover, you get 40 more adventures. Having certain items equipped at rollover, using the Wild Hare familiar in combat adventures, and having certain campground items installed will increase the number of adventures gained at rollover. A complete list of useful items for rollover is at Extra Rollover Adventures. Suggestions for adventure-giving equipment based on your level of gameplay can be found at Maximizing Your Rollover Adventures.
There is no limit to the number of adventures you can play between rollovers. However, you are limited to 200 adventures after rollover is completed. Excess adventures are simply lost forever.
On your character sheet, you can see how many turns you've played in a given ascension, as well as how many adventures you've played since the start of the game.