Stampinwithfab has it correct. ch4 means to make a chain of 4 stitches. When followed by (count as dc and ch1) this indicates that you are using the first 3 sts in the chain in place of a dc or double crochet st. The remaining ch will be a spacer stitch used as part of the design.
Your next instruction probably included dc (double crochet) in next st and ch 1 and potentially repeat to the end of the row. This will give you a spaced pattern of dc sts that are held apart by the ch spacers. This is a pretty standard increase technique for crochet patterns.
When you get to the end of the next row, or if you're crocheting in the round the end of that row, your instruction will read along the lines of connect with sl st (slip stitch) in the 3rd ch of the beginning ch 4. This will ensure that the spacer ch is left in place to complete the pattern on that row.
Hope that helps.