To activate Lots in your Tender you simply select the option 'Use lots' whilst creating a Tender. 

If the Tender was created without lots, but you still want to activate them, you can do so under the 'Tender Definition' tab on the 'Tender Properties' page. Click 'Edit';  and Activate lots.
Note: this can only be done in the preparation of the tender.

After activating the lots, there is an additional tab is created under 'Tender Properties page. Here you can add new lots to the Tender with a name and short description. Consequently you further prepare your lots by opening them from this same page or clicking on the link in the upper left part of your screen (below the Tender name) on: 'Overview Main tender and lots'.