This tutorial will show you how to adjust letter spacing between specific pairs of letters in GIMP, a process known as kerning. Note, however, that this is a hacky approach that is only suited for use with very small amounts of text, such as the main wording on a company logo design.
Before pressing on I really would advise against producing a logo in GIMP unless you are 100% certain that you'll only be using it on the web and not in print. If you think you may, in the future, need to produce your logo in print, you really should design it using a vector-based application like Inkscape. Not only will this give you the flexibility to reproduce the logo at any size, you will also have more advanced controls available to edit the text.
However I do know that some people will be determined to use GIMP to produce a logo and if that applies to you, then this technique will help to ensure that the text content of your logo is as well-presented as possible.
GIMP is a very powerful image editor that also offers enough text controls to allow users to produce designs such as single side leaflets and posters. However it is an image editor and ultimately its text controls are a little limited. A common feature of vector line drawing and DTP apps is a kerning feature that allows you to adjust the space between pairs of letters independently of any other text. This really only becomes important when setting text on logos and headlines, which is something that some users will want to do using GIMP. Unfortunately, GIMP only offers the option to adjust letter spacing universally and while this can be useful to help squeeze multiple lines of text into a constrained space, it doesn't offer the control to kern letters independently.
Over the next few steps, I'll show you an example of this common problem and how to adjust letter spacing using GIMP and the layers palette.