It is very common for longer repeated sections of music to be repeated exactly until the last few measures. A piece with this time signature would be "in three four time" or just "in three four". Two four time Three eight time Six four time. Flags are often replaced by beams that connect the notes into easy-to-read groups.
Four sixteenths equal one quarter and so on. A dotted quarter note, for example, would be the length of a quarter plus an eighth, because an eighth note is half the length of a quarter note.
Unlike the key signature, which is on every staff , the time signature will not appear again in the music unless the meter changes. When this happens, the repeat dots will be put in an ending. This is the incorrect assumption you're making.
And why are you 3 grades behind in theory anyway?
See the chart below which examines the subdivision. It is simply 1 Sixteenth note 2 beams on the stem joined to an Eighth note 1 beam on the stem joined to another Sixteenth note 2 beams on the stem! Powered by Solo Build It! Meters in 6, 9, and 12.
But, as Dom says below, a "whole-note" is only four-beats long when the time-signature equates to four crotchet quarter beats; i. Follow simonhorsey. All of these things affect how much time the note is given in the music.
The lines dividing each measure from the next help the musician reading the music to keep track of the rhythms. So why is one time signature chosen rather than another? The Whole note is the longest music note in general use today.
There are also half rests, whole rests, eights rests, sixteenth rests, etc.