To join sheet bodies use the sew command. If the sheet bodies enclose a volume, a solid is created. If a solid body is your goal you may find it easier to create the solid first and trim it away with your sheet bodies (kind of like sculpting, start with a large block and then create trim tools to get your final shape).
A couple of important things to note for beginners. Under Preferences -> Modeling there is a setting to toggle between Solids & Sheets. If this setting is toggled to Sheet & you try to sew, the enclosed volume will not fill in to create a solid, but rather remain a "shell" body of sewn sheets.
say you have 4 lines/curves connected you can use thu mesh curve or thru curves to make a sheet
when you have multiple sheets and want to join them together
go to insert/feature operation/sew
thru mesh curve and thru curve is found in
insert/free form feature
I'm not picking on you (honestly I'm not) but you don't have to have connecting curves to create any Through Curves or Through Curve Mesh features. The curves only have to be within the Distance Tolerance & not connected.
I say this because it's important for users to understand how the Distance Tolerance works & when it's used.
I may be wrong, but I think he was only asking how to sew surfaces into larger sheets & eventually solid bodies, not how to create surfaces.
Yes you can....that's what the distance tolerance is for....to approximate a sheet through the curves. And WHERE did I say that I personally did that? Re-read my post.
UG's tolerance is there so that IF it needs to use it to create a body, face or edge, it will use it.