If you want to add additional fields for profile and registeration pages in Drupal-7 follow following steps:
1) Enable (if not enable) the Profile module from Admin -> Module.
2) Go to Admin -> Configuration -> Account settings -> Manage Fields.
[caption id="attachment_872" align="alignnone" width="300"] Drupal 7 - adding custom fields[/caption]
You will see "Add new field" label. Enter Label for new field and data type for it (it will be as per your requirement. It can be a text field or radio button or a drop down.)
[caption id="attachment_873" align="alignnone" width="300"] Drupal 7 - adding custom fields[/caption]
Click save button and follow the instructions after it.
3) After filling all required information for the field it will get added to the list.
Below is for "text" field type:
"Maximum length" : Max length that can be stored.
"Required field" : As it is a mandetory field for user. Means user need to provide value for it while submitting the form.
"Label" : You can modify lable here also.
"DEFAULT VALUE" : Need to populate any value when page is get loaded.
"Size of textfield" : size of field as how long it should display the data.
Click save button after setting all values (these all are optional). Now you can see your field in "Manage field" tab.
4) Now go to "Manage Display" tab and define the position or sequence by dragging the field up and down.
5) Now if you visit registration and profile pages you can see your new field their.