Typically, you merge (or join) elements of geometry that have been split. You can only merge like elements, for instance you can merge arcs to arcs, and lines to lines, but not arcs to lines.
To merge 2D geometry,
1. Click Modeling and then, in the Modify 2D group, click More.
2. Click Merge 2D in the Tools section.
3. Click or box the geometry elements to be merged.
Merge 2D in the Tools section.
to complete the operation.