Hello Morteza,
Apologies if anything is lost in translation. If you already have the weldment drawn up and saved out into the correct folder you can draw a 3D sketch and using the weldments tab you can add structural members to each line in the sketch. If you need to add a new weldment i have recently added a tutorial explaining how this is done; https://grabcad.com/tutorials/how-to-make-custom-weldments-in-solidworks
Assuming when you say ISO format you want the file interchangeable between cad systems you can save out the finished structure as a STEP file which will allow you to open up the file in other systems. If you mean something else by ISO format i again apologize for misinterpreting the question.