Before you publish your file on the Internet, you want to test it.
Testing files in Flash, or any web project for that matter, should be done “early and often”. This will help you find problems earlier on, so they are easier to fix.
To test a file you can press CRTL+Enter (Windows) or Command+Return (Mac) to preview in Flash.
To test inside of a browser, choose File > Publish Preview > Default (HTML). Then it will display in your default browser.
The Bandwidth Profiler
This tool helps you find when/where/which frames have a lot of new content, and could take a while to download. This can be used to find frames which are hanging up (if you don’t have a pre-loader).
When you Test a Movie, you can specify a test speed (View > Download Settings > [speed]) This will let you simulate the speed of a user downloading your movie. (Assuming they have a good and accurate connection speed. Actual connection speeds may vary.)
Publishing a Movie for the Web
File > Publish Settings
This allows you to change what Flash player/AS version to you. I recommend using the lowest that you can, so to be compatible with the most number of people.
Under the HTML settings, there are many things you can change to control how items look. Quality, scaling, etc.
Once all the configuration is completed, you will need to upload all the necessary files (HTML, SWF, External SWF, JPGs, etc) to the server, and test.