Accessing IPA characters when using Charis SIL

xunicode (loaded by fontspec) contains the definitions of tipa.sty:

\documentclass[12pt]{article}
\usepackage{fontspec}

\setmainfont{Charis SIL}
\begin{document}
Blowzy DJ frumps vex a knight QC

\textturna

\textipa{[\!b] [\:r] [\;B]}
\end{document}

You can use the IPA characters (of course you need that your file is encoded as UTF-8)

% -*- coding: utf-8 -*-
\documentclass[12pt]{article}
\usepackage{fontspec}
\setmainfont{Charis SIL}
\begin{document}
Blowzy DJ frumps vex a knight QC

ɳ (U+0273), ɲ (U+0272), ʁ (U+0281), ɱ (U+0271), ə (U+0259)

\end{document}

I always recommend that my students learn to use a Unicode IPA keyboard overlay. I've used the Keyman and MSKLC keyboards for Windows, but there are Linux and Mac options available at that page too.

When the keyboard is turned on, certain keys (=, &, <, >, etc.) are activated to modify the key that's pressed next in fairly consistent ways. For example, in the Windows MSKLC keyboard, all retroflexes use <, ^ is used for superscripts, tonal accents are produced with @ followed by a number, and = gives what seems to be the most frequent derivative from a given letter (ɑ for a, β for b, ç for c, ð for d, ə for e, etc.). This semantic key assignment means that you don't have to memorize every shortcut. These shortcuts also work for useful accents/diacritics that aren't strictly IPA: ç č ñ ö, etc.

As long as your editor allows Unicode input (most do these days) and you're compiling with XeLaTeX or LuaLaTeX, you can just use the IPA keyboard to type directly into the editor just as you can in most other applications. You can also copy and paste your Unicode text from other applications too.

The IPA pickers mentioned in the comments on the original question are fine if you don't have to use diacritics or IPA symbols regularly, and they're certainly the best option if you need to use someone else's machine that doesn't have an IPA keyboard loaded.