To create custom fields for account, you need to follow just a few steps:
Click on Accounts submenu from CRM module.
Click on
from the right side of the page then click on CRM settings
Scroll down then click on
then add a name insead of Fields text.
To create custom fields for contacts you should follow first two steps from above then click on Contacts submenu, and only then you should do the exact things from step 3.
You can also delete the custom field by clicking on
icon.