I know it is a combination of red, yellow and blue

There are many different browns, and yes, all of them are obtained by mixing all three primary colors together.

A good way to make brown is by starting with orange, or a rust orange, and adding a navy blue, drop by drop, until it is a suitable color. It's easier to mix a dull sort of color if you start with duller primaries. If you are using MX dyes, for example, you might mix the burnt orange known as brown MX-GRN with a small amount of blue MX-2G; both of these dyes are unmixed single-hue dyes which are available from many of the dye suppliers listed on my Sources for Supplies page, using the chart of pure unmixed MX dyes on my site to pick out the single-hue dyes for use as mixing primaries. You can, of course, prepare similarly hued mixtures using the printer's primaries of cyan, or turquoise MX-G, magenta, or red MX-5B, and yellow MX-8G. All dye suppliers carry these dyes, as well. It's often handy to keep on hand the duller colors for mixing purposes, though, as otherwise it can sometimes be quite difficult to get a truly dark color.

You can get more of a mahogany brown by starting with a dark red and adding green to it, but this is a less satisfactory approach in dyeing than in painting, since neither a pure dark red nor a pure green are available among the commonly-used types of fiber-reactive dye. You must mix your reds by adding orange or yellow to your magenta, and your greens by adding yellow to your navy. It all comes down to mixing all three primary colors, as always, when preparing browns.

What kind of a brown do you want? There are hundreds of different browns you can mix, using the twenty or so available MX dyes.

what kind of brown,
there are two that I would like
the first is the brown like in a box of crayons
the second is a cinnamon brown like the spice
thank you
you are a valuable resource

The one thing you need, beyond the advice already given, is to play with Olli Niemitalo's amazing Dye Mixer Applet . It allows you to get an idea as to what relative proportions of which MX dyes to use to get a certain color mixture.

One caveat is that the Dye Mixer Applet gives quantities by relative weight, rather than volume, so you cannot translate directly to teaspoons of dye, if that's how you usually measure your dye. Different dyelots are standardized to have a certain amount of the active ingredient by weight, not by volume, so this is the only way it can be done. Even if you are not going to be measuring by weight, though, the Dye Mixer Applet is an enormous help.

In order to determine which of the dyes in Olli Niemitalo's Dye Mixer are available to you, see my chart of pure unmixed MX dyes. Make a list of which of the dyes there you have in your possession, and select those dyes in the Dye Mixer. Note that there are several unavailable dyes in the dye mixer, such as Procion brown MX-2R and the various greens; there are no unmixed greens or blacks in the MX line.