Drawings (illustrations) submitted with a provisional application can be informal.
That is to say, they do not need to be in any standardized form.
However, the USPTO strongly recommends submitting specific drawings that adequately depict your invention.
This is because detailed illustrations make it easier for the USPTO to later associate a corresponding Non-Provisional Application you file with this earlier filed Provisional Application.
Further, if drawings are necessary for someone skilled in the field of your invention to practice that invention, the drawings you include in your Provisional Application must be detailed enough to do so.
If the drawings filed with your Provisional Application fail to meet this requirement, any corresponding Non-Provisional Application may not receive the Provisional Application's priority filing date.
LegalZoom can also help you obtain professional top-quality illustrations.
Please refer to the Education Center, "Drawing(s) of the Invention" under the "Filing Requirements for Provisional Applications for Patent" header.