Inc: To increase in crochet, you simply work more than one stitch (number of stitches specified in the pattern) into the same hole, thereby increasing the number of stitches in the current row versus the previous row. To see this being done, please see this video:
Dec: To decrease in crochet, you work the first stitch (the type of stitch -- sc, dc, etc -- should be designated in the pattern) as you normally would, skipping the final step of that stitch (skip the part of the stitch process where you draw a final loop through the loops on your hook and end up with one single loop on your hook, ready to work the next stitch), leaving the worked loops on the hook. Then work the next stitch as you normally would, with the previous stitch's loops still on the hook. When you get to the end of making this second stitch, draw your yarn through ALL of the loops of both the first and second stitch to draw them together. You will see that you now have one less stitch in the current row than you did in the previous row.