Spider Solitaire Blue offers the three classic difficulty modes: one suit for learning, two suits for a real game, and four suits for a genuine challenge. The goal is to build descending sequences from king to ace in a single suit, at which point the sequence is removed.
The rule that defines it is the dealing restriction — you cannot deal from the stock while any tableau column is empty, so empty columns are both your most valuable resource and something you must spend before continuing.
How many suits the deck uses. One suit is a gentle introduction, two is the standard game, and four is substantially harder because same-suit runs are far rarer.
Because you must fill every empty tableau column before dealing. It's the rule that makes empty columns both valuable and temporary.
Yes — tap or drag cards. Nothing to install.