Do you need a DBA and an LLC to start a business?
You do not need both a DBA and an LLC to start a new business. Let me explain.
An LLC is a type of entity with limited liability. It is similar to a corporation or an S-Corporation. LLCs are officially registered with the state in which they get formed under a separate name. Meaning that you, Trevor, can register an LLC called Trevor's Ventures LLC. Once registered, an LLC can just do business under its own name, without bothering to get a DBA.
You will only need a DBA in one of two cases. First, if you decide to do business through your LLC, Trevor's Ventures LLC, but under a different name, such as Trevor's Donuts. Then you need to register Trevor's Donuts as a DBA for Trevor's Ventures LLC.
Second, if you decide not to form an LLC at all, but instead continue to do business by yourself, as a sole proprietor. Then if you want to call yourself in business by any name other than your own, such as Trevor's Donuts, for example, you will need to register that new business name as a DBA for yourself.