Q1. If you are using QlikView integrated with Windows Active Directory (is that what you mean by LDAP?), then there is no need to create users and groups again in QlikView. QlikView recognises who you are from your windows logon when you navigate to Access Point - you will see "Welcome [your logon]" in the top right of the window. QlikView then works out what applications on Access Point you are allowed to see based on the windows file permissions of the QVWs sitting on the server. If you want to grant a user or AD group access to a QVW, then simply assign read access using the file properties.
Q2. The whole idea of AD integration is to achieve single sign on (SSO) and thus avoid having to maintain users and permissions in QlikView as well as your network. However you can choose not to use AD integration and maintain a list of users and groups in QlikView. Or you can create a second set of manually maintained users in conjunction with users in AD.
Your network logins already exist in AD. Setup is required in QlikView, using the QlikView management console (QMC). Basically you define whether you want to allow user CALs to be automatically assigned to users, or whether you want to manually grant them. I would start with reading up on the subjects related to licencing and authorisation in the QlikView Server Reference Manual. If you don’t have the manual you should be able to find it on community.
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