How to link consecutive lines after tool usage

[Anonymous]

Hi. After using mirror, rotate or copy tools, consecutive lines are not linked so the extrude tools work the wrong way around, forcing me to redesign them each time. Also, sometimes I want to break lines to manipulate them but I can't because they are connected, so they are opposite side errors.. can anyone explain me what causes the lines being linked or unlinked?

Thank you.

[jhackney1972]

Could post an example for both types of situations.