There are two drop down lists in
the Line Gallery which effect a selected line or object.The Line Joins drop down has three options the results of which are shown on the left. The yellow dotted lines represent the original unmodified line.
Line Caps
effect the end of a line or path. The Round Cap option rounds the end of the line beyond the actual line. Square Cap also extends the end of the line beyond the actual line by 1/2 the width of the line.
OK, so why would you use any of these Joins or Caps?
Sometimes, if two lines meet at a very tight angle, the Mitered point can be excessive, almost stiletto-like, choosing the Beveled Join
option softens the edge. Round Joins and Caps can soften line art and make it more friendly. Especially at larger point sizes as shown here.