To create a Weldment structure in SOLIDWORKS, you typically follow these steps:

1. Create a new part document.
2. Define a Weldment profile: This is the cross-sectional shape of the structural member you want to use (e.g., square tube, angle iron, etc.). You can either use the default profiles provided by SOLIDWORKS or create custom profiles.
3. Create a sketch: Use 2D sketches to define the outline of the structure you want to create.
4. Insert structural members: Using the Weldment feature, select the sketch lines where you want to insert the structural members and choose the appropriate profile. SOLIDWORKS will automatically add the required end treatments (e.g., miter, cope, etc.).
5. Add additional features: You can add features such as gussets, end caps, and weld beads to enhance the structure.
6. Specify the Weldment cut list: SOLIDWORKS generates a cut list that provides information about the individual members, including length, material, and weld details.
7. Create detailed drawings: You can create engineering drawings with dimensions, annotations, and other necessary information to document your Weldment structure.