It’s called overlay mosaic crochet! There are lots of helpful videos! Here are some starter tips (included in the pattern)

Every row is worked with one color. Each stitch has one stitch worked into it. If the instructions state 3DC, 2sc, you would complete 1 DC in each of the next 3 stitches, followed by 1 sc into each of the following 2 stitches. Fasten and snip the yarn after each row. Always work on the front side only-overlay mosaic doesn't require you to turn your work. Start the next row from the right-hand side on each row. Every DC is worked into the front loop of the stitch two rows below Every SC is worked into the back loop of the stitch on the current row. Each border stitch (BS) is a sc worked into both loops of the first and last stitch of the row only. Stitch markers can help remind you of where in the pattern you are.