Your trademark is officially protected from your application's filing date. However, this rule only applies to those cases when the registration is successful. Once your brand is in the process of obtaining a trademark, you can start using the symbol ™ so that others know that some level of protection applies to your brand. The simple placement of the ™ symbol might prevent copycat attempts.
If you believe some issues might arise during the registration process, such as opposition or refusal, you might want to wait until purchasing and distributing large quantities of your products.
In some countries, such as the US, it is compulsory to start providing your services or selling your goods before the trademark is officially registered. Failing to do so within a certain period will prevent you from obtaining a trademark registration.