Mnemonics

"string","stitch"

• Almost always has something to do with strings or matching

Used alone

~ As a prefix operator, coerces to subtype Str (string)
~ As an infix operator: concatinate or stitch characters together, instead of . in perl5. Specification

Operators containing this character

~^ ~| ~& bitwise logical operations on buffers or strings
~= String Append, the post-assignment mutant form of ~
~~ and !~~ The Smart Match operator and its negated form.

When used inside regexes

~~ and !~~ inside a regular expression: cause a nested submatch to be performed.
<~~ inside a regular expression starts an extensible metasyntax for sub-pattern re-use (and must be closed with >)

Hyper operator and meta operator restrictions

Most hyper operators and meta operators have functional ~ forms.

Old, deprecated, or other language uses

=~ and !~ in Perl5 used to be for matching. Now it is ~~ (see above). =~ is always a syntax error in Perl6.
~ as a prefix operator in perl5 was a logical binary invert. Now that is ~^ or +^.