The number of chains you need may be stated before the first row, or in the first row, depending on the pattern writer. So with the slip knot now on your hook, you will make a foundation chain of a specified length, which the pattern will state.
Here is how to make a slip knot ( See Figure 1 & 2).
Does the pattern tell you this? No - it just assumes you know that! Whatever way the pattern is to be worked, the very first thing you must do is make a slip knot on your hook. A pattern may be worked in rows (that is, back and forth to form a flat piece such as an afghan) or in rounds (worked around to form a tube with no seams, such as a hat). With the abbreviations terms at hand, let’s look at a typical pattern. A complete list of crochet abbreviations and terms and their meaning can be found at: Getting Started