The squiggly line above certain letters is called a tilde. Certain languages require typing a tilde above the letters A, N, or O. While most keyboards have a tilde key, you can't just hold down the key and get the tilde above the letter. You can use the character map function built into Windows to type these letters, even while using a normal keyboard.
Place the cursor where you want to type the letter with the tilde.
Click the "Start" button on the Windows task bar, then click "Accessories." Select "System Tools" and click "Character Map." The Character Map window will open.
Click the icon for the letter you want to add.
Click the "Select" button, then click "Copy."
Paste the letter into the document by pressing "Alt" and "P" or right clicking with your mouse and selecting "Paste."
You can also type the letter with the tilde by holding down the "Alt" key and typing in a special code. For a list of codes, see the link in Resources.