I have made a tutorial for you :)
Here we have 3 surfaces that form a boat hull. Knit surfaces enables us to merge them into 1 single surface.
go to insert -> surface ->knit. Now fill the selection box with the surfaces you wish to knit. Gap control allows you to control how big gaps will be knit shut and how big caps will be left . Gaps bigger than the tolerance will be left open. "Try to form solid" will try to form a solid from enclosed surfaces. The model will look just as it did before the knitting operation but you will now see a single surface listed in the FeatureManager design tree as Surface-knit _n
"Merge entities" merges faces with the same underlying geometry. An example is added - Two rectangular surfaces.
After knitting with merge entities on.