A single augmentation dot is used to notate durations like 3/1, 3/2, 3/4, 3/8, 3/16 3/32 etc.
An augmentation dot adds half the original duration to a note: a dotted 1/8 thus has a duration of 1/8 + 1/6 = 3/16
Augmentation dots are often used to notate syncopated rhythms as in:
Please note that augmentation dots are always written between two staff lines (or leger lines)
Double augmentation dots are sometimes used to notate durations like 7/4, 7/8, 7/16, 7/32 and 7/64
A second augmentation dot adds a fourth of the original duration. A double dotted 1/8 will end up to: 1/8 + 1/16 + 1/32 = 7/32
Augmentation dots can be achieved in two ways.
Select the augmentation button on the buttonbar before entering a note (or <5>) or use the button for note lengthening by 3/2 (or <F6>)
Once more use of punctuation will add another dot and leave the note with 7/4 of the duration. Triple punctuation is not of much relevance so the third time, the duration will be lengthened to 8/4 (instead of 15/8). Punctuation can be made undone with <F5> which will shorten any duration with 2/3 if meaningful.