exploding rectangle to 4 lines?

Object>CompoundPath>Release.

In IllustratorCC Menus, Path > Remove Anchor Points explodes into segments.

(Pls add here, if this is wrong or a better method is available)

A couple of versions back, in Illustrator's typical decades-late fashion, the program finally gained the ability to cut multiple anchorPoints in one move.

This is, of course, hindered by the same basic ill-conceived core interface scheme which is a stumbling block to everything else in Illustrator:  the hideous two-pointer selection scheme and its upside-down "direct-selection" versus "normal selection" distinction.

Without going into the details, in this context it means Illustrator--despite its long-engrained insistence on two separate selection pointers--doesn't know the difference between a path which is selected as an object, as opposed to merely having all its anchorPoints selected.

So while Illustrator can finally, at long last, cut more than one anchorPoint at a time (what a concept), it still can't cut all the anchorPoints of one path at one time. So you can draw a rectangle (or any other path), deselect one of its anchorPoints, and then cut all the others in one move by clicking the Cut Path At Selected AnchorPoints button in the Control Panel. Then cut the remaining one.

Even so, though, using the cut-selected-anchors button avoids another byproduct of Illustrator's poorly-designed selection scheme: the chronic tendency to inadvertently create so-called "stray points." Illustrator is far more inclined to do that than any other program in this category. Creating stray points is the risk you run--and must therefore always be mindful of--when using the various methods of "selecting segments", some of which have been suggested in this thread.

JET

There is no built in feature to explode a shape.

Here's what you can do though.

Use the Direct Selection Tool (The white arrow) to click the center of the path on one side. Edit Copy, then Edit > Paste In Back. Repeat for all 4 sides. Finally, select the the path again and hit delete twice. You will be left with four independent paths.