To register on the Kdenlive web site, create a new account [1] and enter the required information. You will receive your password by email.
Registration offers access to a number of features, including:
Registered users who apply for editing permissions [4] can also contribute documentation [5].
Links:
[1] http://www.kdenlive.org/user/register
[2] http://kdenlive.org/forum
[3] http://kdenlive.org/tutorial
[4] http://kdenlive.org/forum/ask-documentation-writer-role
[5] http://kdenlive.org/contribution-manual/how-write-kdenlive-manual