First you need to create an account to use the bug tracker by clicking here :!default.jspa|!default.jspa

Fill all field and validate your account.

When you validate the form Click here to log in.

You can now create your first issue :

1 : click on "Create Issue"
2 : choose the project : PrestaShop version 1.4 or 1.5, Prestashop Native Modules & Themes
3 : choose the issue type : bug or improvement
4 : Submit

On the next screen fill all informations to create your issue.