Use the Browse... buttons to locate the files to be included in the .pk3 file. This utility is intended for the creation of simple, single-model .pk3 files. If you want to include multiple player models into a .pk3 file, you'll just have to learn how to do it manually.
.tik files: You will generally have two per player model: one defining what other people see, and one defining what you see (this file contains _fps in the file name). If you do not include the _fps.tik file, you won't see your hands and arms when you're playing the game. Four filename spaces are provided, so that you can create both Allied and Axis versions of your player model.
.shader file: You should only need one of these.
Face image file: This may be included either in Targa (.tga) or JPEG (.jpg) format. Note that there is a 2MB file size limit when uploading. If your file is larger than that, you're doing something wrong.
When you have filled in the appropriate fields and pressed the Create PK3 File button, your browser will upload the files to the server, which will then put them into an appropriately structured .pk3 file. Your browser should then begin downloading a file named "Rename_This_File.pk3". Save it to your MOHAA "Main" directory, altering the name to reflect the contents (such as the skin name with a .pk3 extension). Once the transfer is complete (or aborted), the files you uploaded will be deleted automatically from the server.
You must include at least one .tik file, plus one .shader and one face image file. If you do not do this, your upload will fail. If you attempt to put more than one filename on a line, your upload will fail. If you attempt to upload files larger than 2MB, your upload will fail. If you think you're doing everything correctly and receive an error message, hit your browser's "Back" button and try submitting again. If you still receive an error message, you may email me for help. Be sure to tell me the names of the files you're attempting to upload, and their file sizes.