Question about repeat signs.

The ones in the palette work the same, they have different display options set.

You can always use the first one if you want to rather than the second one, though I see the second one much more often. If there is a third ending, you will always use the first one to show how far the second ending goes.

The first one is usually used before a repeat, hence it is "closed". The 2nd one implies "take this and go on".
:)

Note that since MuseScore 2.1 those no longer behave the same, but regardless of which one you enter into the score, you can turn it into the other using the inspector.

The closed one only applies over the span it covers.
The open ended is in effect past the end of the symbol, until a reason to stop applying it is encountered in the notation.