Run maketorrent. (See this section of the FAQ if you haven't installed it.) If you are sharing a single file, click the (file) button, otherwise click the (dir) button. In either case a file dialog will appear, and you should select the file/directory that you wish to share.
Enter the tracker's announce url in the space provided, or use the drop-down list to select from one of a common list of trackers. Remember, if you use a site's tracker when creating a .torrent file, plan to upload/post the file to that community. You can also add a comment, but it's optional.
Select the piece size, or just accept the default value of (auto). In general, the smaller the piece size, the more efficient the BitTorrent download will be, but will result in a larger .torrent file. 256 kB seems to be the most common piece size in use these days, but you can experiment with other settings if you want. Avoid very large piece sizes for small files; likewise avoid small piece sizes for very large files.
Click create torrent to begin the process of creating the file. You can then select if you want to create a single .torrent for all the files in the directory, or a number of separate .torrents. Most of the time you want a single .torrent for the whole folder, unless you know what you're doing. When finished, you should find a newly created .torrent file in the same directory as the file/directory you selected to share.
Upload this .torrent file to a web server. Usually this means going to the web page of the site whose tracker you used and clicking the "Upload torrent" link. The procedure varies from site to site, but it's usually always explained in a FAQ link or forum posting. If you are running your own web server (and have configured it appropriately) then upload the file to your server's public web space, or whatever method you use to put files on your server.
Finally, you must seed the file. Until this step, nothing but metadata has been transferred. Seeding is necessary to actually transmit your file to others. There are several ways to do this, but the simplest is to use your ordinary BitTorrent client just as you would with any other file. Navigate to the page on the web server where your .torrent is posted, click the link, and when the BitTorrent client starts be sure to select the same file/ directory that you used in maketorrent in step 2 above. The client should check the files and verify that they are complete, and then connect to the tracker and begin seeding. There are several important points about this step: