In most versions of the game the available gestures are:
(Please note that while the following text attempts to cover rules in general, examples provided are mostly based on Warlocks spellbook, and the spells are referenced accordingly.)
Each turn, each player can show one of the gestures in their left hand, and the same or a different gesture in their right hand. For example, D/P stands for pointing the left hand digit and showing the palm of the right hand. Some spells require both hands to perform the same gesture on the same turn; for example, clapping is only useful if done with both hands (notation for that would be C/C, or c for short). For example, to cast Invisibility, a player needs to gesture PPWS with one of the hands, and ??WS with the other (notation PPWS/??WS or ??WS/PPWS or simply PPws).
Some spells can have multiple gesture patterns. Specifically, Counter Spell can be cast either with WPP or WWS, and (under Warlocks spellbook) Blindness can be cast either with DFWFd or DWFFd.
Please note that sequences needed to cast spells can overlap; for example, sequence PSDF casts Shield (P) on turn 1, Magic Missile (SD) on turn 3, and Charm Person (PSDF) on turn 4. Likewise, DPPSFW will cast Amnesia (DPP) on turn 3, and Summon Ogre (PSFW) on turn 6.
If several spells can be cast as the result of gestures shown, unless the player specifies the intended spells in their orders, spells ending with two handed gestures will be prioritized, and after that spells with longer gesture patterns. For example, sequence PPWS/WWWS by default will cast Invisibility (PPws from both hands) and not Counter Spell (WWS from right hand), unless the player selects spell Counter Spell for the right hand and does not select Invisibility for left hand.
Besides spells, there are two special actions that players can perform. The first one is showing two palms (P/P or p) to signal Surrender. This is not a spell, so if the gestures are shown, the player surrenders (if they are still alive by the end of the upcoming turn and if there are any opponents to surrender to) nonwithstanding other spells and effects, including Dispel Magic (which prevents all other spells from being cast). Please note that in some situation you might not be in full control of the gestures that will be shown by you next turn (for example, if you were charmed last turn, your opponent will chose your next gesture for one of your hand) - in such situation attempting to show P in one of the hands might lead to a surrender, even if it was not the intention.
The second special action is 'stab', which will be displayed as '>' gesture. This special action deals 1 damage to any target; however, stabbing would break the sequence of your gestures, which is generally not a good idea. Each player only has one dagger, so attempting to stab with both hands (>/>) will result in stabbing with the right hand. Under SpellBinder spellbook a player cannot stab themselves.
Failure to show any gesture (as a result of own negligence or of the opponent's spell) would result in a break in the spellflow, displayed as '-'.
Most spells and actions have the desired effect when cast at a specific target (self or opponent or a monster). When summoning a monster, target the spell at a player that you want to be able to control this monster (normally that is yourself) or at a monster that player already controls. Most of the spells will fizzle (do nothing) if cast at 'nobody' or at a target that was not summoned.
Countering or targeting regular monsters (goblins, ogres, trolls, giants) can be a little bit tricky at first. If your opponent plans to Summon Ogre on the next turn (has PSF ready in their left hand) and you are ready to kill it with Cause Light Wounds (your have WF ready in your right hand), you want to gesture P with RH and target the monster that is being summoned from opponent's left hand. This way, ogre resolves first (having spell priority 5), and then Cause Light Wounds resolve (having spell priority 33), finding the target and killing the Ogre (unless opponent has also protected the ogre by some other means, for example, casting Cure Light Wounds at the same monster with their other hand). However, if you intend to counter the upcoming ogre (you have WP ready in your right hand), targeting opponent's left hand will fail miserably (Counter Spell, having spell priority 2, will resolve before the Ogre, will not find its' target and fizzle, and the ogre will be successfully summoned after that); instead, set opponent as the target for your Counter Spell, so that your opponent will receive magic shield, which will nullify most of the spells cast at them this turn (including their ogre).
However, some spells will successfully resolve even if cast at 'nobody':