There are several tools that are specifically designed for marking your patterns.
Why do you need to mark your patterns? Well, adding marks (notches) to your armhole and sleeve helps you to set the sleeve properly (and in the correct armhole!.
These tools are nice to have, but not really necessary. I've included them in the event you want to explore a few more professional pattern drafting tools.
Click on the images, below, to go to the item in Amazon. As an Amazon Associate I earn from qualifying purchases. This helps to keep this site free for your use. You are free to search Amazon for these or other similar items without using the affiliate links on this page.
A pattern notcher cuts a nice, rectangular notch into your patterns, allowing you to match two pattern pieces along the seam line.
Notches, for example, help you to set the right sleeve into the right armhole, with the top of the cap properly placed at the shoulder seam.
You can clip tiny "V" notches with your paper scissors, too, but if you make a lot of patterns, this is handy to have.
An awl comes in handy for marking points, like the ends of a dart. You'll also use a point, rather than a notch, for marking where a collar, for example, turns a corner.
You can also poke a hole in your pattern with the tip of a sharp pencil, but be careful not to tear your paper too much. The awl makes a cleaner hole in the paper pattern.
A tracing wheel doesn't actually mark your pattern; it transfers your markings (especially straight lines, like the lines of your darts) to the wrong side of your fabric.
This one, with relatively long, needle-like prongs, is much more effective than the little plastic wheels you find so often in the fabric store.
Tracing paper is used in conjunction with the tracing wheel. This package has a variety of colors, which will show up nicely on fabrics of dark or light color.
My preference for marking is tailor's wax. It is often referred to as tailor's chalk, but be sure that you are getting the wax style, not the true chalk (which I find more difficult to work with).
The wax acts as a crayon (use the sharp edge for drawing lines), and melts away when the fabric is ironed.
The drawback, of course, is that you lose your markings if you need to press the garment but still need your lines.
The wax can also leave a mark on your fabric, so test a swatch first. Tailor's wax is also available in colors, but they DO stain light colored fabrics, so be very careful when using them.
The true tailor's CHALK does not melt or stain your fabric, but can be more difficult to see, and it rubs off as you are working on your sewing.
The "nice to have" tools:
ClothingPatterns101.com does not sell the personal information of its users to anyone, ever.