The formal name for ~ is tilde.
Many programmers call it twiddle.
A slash or forward slash is /. If north is at the top of the page, it points southwest-to-northeast. It is tilted the same way that most right-handed people slant their writing, so it has a "forward" slant. Standard American keyboards have ? as Shift-/.
A whack or backslash is \. If north is at the top of the page, it points northwest-to-southeast. Standard American keyboards have | as Shift-\.
See also "What do programmers call these punctuation marks? (Parentheses, brackets, ticks, etc.)"
The ASCII entry in The New Hacker's Dictionary, as edited by Eric S. Raymond, includes English-language computer programming names for many common symbols.