To attach bait to a fishing rod in Stardew Valley, follow these steps:

• First, you need an upgraded fishing rod that supports bait. The starting Bamboo Pole cannot equip bait. You must have at least the Fiberglass Rod (unlocked at Fishing Level 2) or the Iridium Rod, both of which have slots for bait

• Open your inventory and select the bait item. Then, drag and drop the bait onto the fishing rod in your inventory. Alternatively, you can right-click the fishing rod while holding bait to attach it (on PC). On consoles like Switch, use the appropriate button (e.g., Y on Switch) to "use" the bait on the rod

• Once bait is attached, it will increase the bite rate of fish, making fishing more efficient.
• To remove bait, use the same method: right-click or use the action button on the rod with bait equipped.

In summary, you cannot attach bait to the Bamboo Pole; you need a Fiberglass or Iridium Rod. Then, in your inventory, use the bait on the rod by dragging it onto the rod or using the "use tool" action (right-click or equivalent button)