To earn the "Tiny Puzzler" trophy in Pic-a-Pix Color, you simply need to finish any puzzle with a 5x5 grid, which is the smallest puzzle available. Go ahead and load up the first puzzle, which depicts a tree.
If you're unfamiliar with how Picross works check out the Info button on the game's main menu. Essentially, you need to fill in the squares to correctly fulfil the requirements of each row and column. Each coloured number next to a row or column describes the amount of consecutive squares that should be painted that colour, somewhere in the row.
The numbers are in order -- if a row description states 1 red, 1 green, 3 brown left-to-right, the final image will match those requirements left-to-right. Similarly if a column description states 1 red, 1 green, 3 brown top-to-bottom, the final image will match those requirements top to bottom. It's easier to understand once you start trying it, but the only other major rule to bear in mind is that if you have two numbers of the same colour next to each other, there must be at least one blank space between them (e.g. if the description says 3 black followed by 2 black, there must be at least one blank space between them -- otherwise it would say 5 black).
You can cycle through the colour palette on the top left with the shoulder buttons. Use
to paint a square (double tap to erase) and use
to mark a square as a blank (it'll put an X in the square, but the final image will show these as white assuming you do it all correctly).
You'll find all of the 5x5 solutions in the below Google Drive folder. (Eventually this will contain every puzzle in the game).
https://drive.google.com/open?id=1GouHjmn9DNF034KII1A96lGLKD...If you complete any of the 5x5 puzzles in less than 15 seconds you'll also get: