A sigil is, in short, a magical symbol. Traditionally there are many g=sigils in books that you can explore online or at a library. A quick search will yield a wealth of information about traditional sigils and there uses. What I will be discussing today however is not these established sigils but ones you can create on your own with the variety of methods outlined here.
First, I will provide a number layout table and then a table assigning values to letters.
Using this method, you can write a short intention such as I have power. or I can see. These should be declarative sentences of actions or circumstances. Every letter is assigned a number on the table.
Then you draw lines between the numbers as shown above.
A similar method is used with a number wheel. In some methods repeating letters are removed or, in others, they are marked with a special symbol in the sigil.
The final method is far more standard and used by most witches. It is called the sigil wheel.
Once you have a basic form you can orient it, add to it, or subtract, from it to make it your own.
Now where to put a sigil? Anywhere and everywhere. My mother has carried a sigil I created for g=her 24 years ago on a slip of paper in her wallet. I have cleaned my house many times using sigils in vinegar to clean the windows, floors, and many household surfaces. You can also use roller ball perfume to write them on yourself. Essentially no one must know these wards or symbols are there save yourself.
Sigils can be powerful but remember as you are creating them to empower them with intention and belief. The most powerful part of magic is intention, and your most powerful tool is visualization. Visualize your intentions manifesting. You will see amazing things happen.