Use the principle one person one password. Don't even share your password with the rest of your family. You can't be sure what your kids and their friends are doing. This is very important if you are using Internet banking. If something goes wrong, your bank will probably not accept losses if you share your password with someone else, even if it is a family member.
Many people use the Internet for buying goods like books, CDs etc.
Preferably use only systems with specific safeguards. Always check your bills from credit card companies and banks. Don't leave the receipt in the shop. Bring it with you. Copyright laws in most countries cover computer software.