Go into Lightroom and select the photos that you want to upload to your SlickPic gallery.
When you have selected the photos you want to add, click Export.
The following window will open where you can choose some parameters for your images.
Select the location where you want to save your photos and give your subfolder a name.
Fill in any of the other parameters as you require. By default, the original photo size will be downloaded.
You will to monitor your download via a bar in the top-left corner of the screen.
Then, go to the Organizer in SlickPic and click Upload.
Click Select files from your computer.
Locate the files on your computer and click Open to add them to your SlickPic gallery.