Feature-based Models
Just as an assembly consists of individual parts, a SolidWorks part consists of individual features.
The first feature you create in a part is the base. This feature is the basis on which you create the other features. The base feature can be an extrusion, a revolve, a sweep, a loft, thickening of a surface, or a sheet metal flange. However, most base features are extrusions. The following are some of the features you can use to make parts in SolidWorks.
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Extrude - Extrude creates a feature by extruding a 3D object from a 2D sketch, essentially adding the third dimension. An extrusion can be a base (in which case it always adds material), a boss (which adds material, often on another extrusion), or a cut (which removes material).
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Revolve - Revolve creates a feature that adds or removes material by revolving one or more sketch profiles around a centerline. The feature can be either a solid, a thin feature, or a surface.
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Loft - Loft creates a feature by making transitions between profiles. A loft can be a base, boss, cut, or surface.
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Sweep - Sweep creates a base, boss, cut, or surface by moving a profile (section) along a path.
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Boundary - Boundary creates very high quality, accurate features useful for creating complex shapes for the consumer product design, medical, aerospace, and mold markets. A boundary can be a base, boss, cut, or surface.
SolidWorks features are of two types: sketched and applied.
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Sketched features such as extrusions, revolves, sweeps, and lofts are based on sketch geometry. 
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Applied features such as chamfers, fillets, and shells are applied directly to the model.
SolidWorks features are always added to the model, whether they add or remove material. You can modify features after creating them. Use the SolidWorks Defeature tool to remove details from a part or assembly and save the results to a new file in which the details are replaced by dumb solids (that is, solids without feature definition or history).
See SolidWorks Tutorials: Lesson 1 - Parts
See SolidWorks Tutorials: Revolves and Sweeps
See SolidWorks Tutorials: Lofts
See SolidWorks Tutorials: Fillets