The controls below are universal across all FX units in Serato Studio.

Show/Hide FX Panel: Click on the FX button to reveal the FX slots in the space between the Library panels and the Deck view / Scene Player or Song view.
In the Master Track view this will appear below the main waveform.

FX Header: Shows the name of the selected Pad, Deck, or Track and indicates specifically where FX in these slots will be applied. This will either be positioned on the left or right of the FX slots.
Note the color of the title in the header will change, in the case of Deck Pad FX, to help quickly identify which Pad has been selected.
Hover your cursor above the Header to allow the title to scroll.

FX Toggle: Click on the title of the FX in the slot to enable it, which is indicated by the inserted FX unit turning purple.
Click on it again to disable it, indicated by the FX unit turning light grey.

FX Depth: Controls the level or amount of the FX that is applied. Note the notch inside the knob will change color, based on the selected Pad, in the case of Deck Pad FX.
Click & drag on the knob to adjust the value, or hold [command ⌘] (macOS) / [ctrl] (Windows) on your keyboard while doing so, to make finer adjustments.

FX Slots: Drag & drop FX from your library, directly onto an empty FX Slot, or use the FX Select function to insert FX.

FX Select: Click on the small white arrow on the right-hand side of the FX slot to reveal the FX Select list drop-down.
Mouseover a category to reveal and locate your desired FX.
Click on the arrow near the bottom of a list, to expand the list, if truncated.

Add FX Slot: Click on the + icon on the right-hand side of the FX Slots, to add a new FX Slot.

FX Scrollbar: Click, drag, and release the FX scrollbar to reveal FX Slots that are no longer in view.

Reorder FX Slots: Click and drag on an FX Slot, then release it over another slot, to change the order of your FX Slots.
Changing the order of FX Slots, which work from left-to-right will change the way FX are processed, which will modify the resulting sound output in that chain.

FX Beats: Displays & allows for adjustment of the currently selected value for time-based FX.
Click on the small arrows on either side of the timing to cycle through the different timing options.

Cut, copy, paste & delete: Right-click on the edges of the FX Slot (any area aside from the title of the FX or the FX Depth), to reveal the aforementioned options.
Copy or cut an FX Slot and then paste it into another position or FX Slot area from different Pads, Decks, or Tracks.
Choose Delete to remove an empty or populated FX Slot.
NOTE: You can also left-click on an FX Slot to highlight it (indicated by the white outline around the FX Slot), then either use the [command ⌘] (macOS) / [ctrl] (Windows) + C (copy), [command ⌘] (macOS) / [ctrl] (Windows) + V (cut), [command ⌘] (macOS) / [ctrl] (Windows) + P (paste), or DEL (delete) keyboard shortcuts, or the respective aforementioned commands from the Application Tool Bar : Edit menu