Use the small buttons above a 4 to add √ (square root) or ! (factorial, 4!=24). Then drag +, −, ×, ÷ from the symbol palette below into a slot. To join two numbers with no symbol between them, like 44, drag in the "44" tile. Want to calculate a pair first? Try the "Group" buttons too.
Four Fours is a classic recreational math puzzle: use the number 4 exactly four times, combined with only the four operations (+, −, ×, ÷), to build whatever number you're given. The constraint of repeating just one number, 4, is exactly what makes for such a wide variety of challenges.
The four operations alone can't reach very many numbers, so this puzzle also lets you use √ (square root), ! (factorial, 4!=24), and a "44" tile that joins two 4s together with no symbol between them. Add in the ability to group a pair and calculate it first (like parentheses), and the range of numbers within reach grows a lot wider.
There's often more than one way to make the same number, so once you build the target number, take a moment to ask "is there another way?" too. If you get stuck, the hint button will show you an example answer.