Cards Connect is a connection-matching puzzle: find pairs of identical cards that can be joined by a path of no more than three straight lines, with no other cards in the way. Each match adds time to the clock, so a good run sustains itself.
The three-line rule is what makes it a puzzle rather than a memory test — two identical cards in plain sight can be unmatched simply because the route between them is too convoluted.
A pair can only be matched if you can draw a path between them using at most three straight segments, without passing through any other card. It's what makes an obviously identical pair sometimes unmatchable.
Every successful match adds time to the clock, so a steady run of matches keeps the timer healthy.
Yes — tap two matching cards. Nothing to install.