p(x) gets the value of a specified p-field. (So, 'p(5)' and 'p5' both return the value of the fifth parameter in a certain score line, but in the former case you can insert a variable to specify the p-field.
pindex does actually the same, but as an opcode instead of an expression.
pset sets p-field values in case there is no value from a scoreline.
passign assigns a range of p-fields to i-variables.
times / timek return the time in seconds (times) or in control cycles (timek) since the start of the current Csound performance.
timeinsts / timeinstk return the time in seconds (timeinsts) or in control cycles (timeinstk) since the start of the instrument in which they are defined.
date / dates return the number of seconds since 1 January 1970, using the operating system's clock; either as a number (date) or as a string (dates).
tempo allows the performance speed of Csound scored events to be controlled from within an orchestra.
miditempo returns the current tempo at k-rate, of either the midi file (if available) or the score.
tempoval reads the current value of the tempo.
ihold causes a finite-duration note to become a 'held' note.
xtratim extend the duration of the current instrument instance.
metro outputs a metronome-like control signal in a variable frequency.
mpulse generates an impulse for one sample (as audio-signal), followed by a variable time span.
changed reports whether a k-variable (or at least one of some k-variables) has changed.
trigger informs whether a k-rate signal crosses a certain threshold.
if branches conditionally at initialization or during performance time.
loop_lt, loop_le, loop_gt and loop_ge perform loops either at i- or k-time.
init initializes a k- or a-variable (assigns a value to a k- or a-variable which is valid at i-time).
igoto jumps to a label at i-time.
kgoto jumps to a label at k-time.
timout jumps to a label for a given time. Can be used in conjunction with reinit to perform time loops (see the chapter about Control Structures for more information).
event_i / event: Generate an instrument event at i-time (event_i) or at k-time (event). Easy to use, but you cannot send a string to the subinstrument.
scoreline_i / scoreline: Generate an instrument at i-time (scoreline_i) or at k-time (scoreline). Like event_i/event, but you can send to more than one instrument but unlike event_i/event you can send strings. On the other hand, you must usually preformat your scoreline-string using sprintf.
schedkwhen triggers an instrument event at k-time if a certain condition is given.
seqtime / seqtime2 can be used to generate a trigger signal according to time values in a function table.
timedseq is an event-sequencer in which time can be controlled by a time-pointer. Sequence data are stored into a table.
active returns the number of active instances of an instrument.
maxalloc limits the number of allocations (instances) of an instrument.
turnon activates an instrument for an indefinite time.
turnoff / turnoff2 enables an instrument to turn itself, or another instrument, off.
mute mutes/unmutes new instances of a given instrument.
remove removes the definition of an instrument as long as it is not in use.
nstrnum returns the number of a named instrument.
chn_k, chn_a, and chn_S declare a control, audio, or string channel. Note that this can be done implicitely in most cases by chnset/chnget.
chnset writes a value (i, k, S or a) to a software channel (which is identified by a string as its name).
chnget gets the value of a named software channel.
chnmix writes audio data to an named audio channel, mixing to the previous output.