how are you attempting to make your rule? go through your process.
I click Manage Rules - that's what the description on how to create a rule says to do. Is there another way?
There's two efficient ways to create a rule, if that is indeed what you need to do, although assigning in plugin to a Group, as @HadToRegister suggested, is another way of creating a more generalized rule.
To create a specific rule, there is an icon in the Dependencies column in the Plugins tab: you can either left-click it and choose Edit from the little pop-up menu, or you can right-click-and-drag from that icon to the icon of the other plugin to which you need to create the rule.
If you choose Edit, then the icons for all the other plugins turn into checkboxes, and you can check the box of the other plugin with which you need to create the rule. When you check another box, then it creates a Loads After rule for the first one you selected; "loads after" is the only rule direction possible with this method, so the first plugin you choose must be the one you wish to load last of the two. If you hover over a checkbox, it will display a tooltip showing what rule will be created by checking it. Unfortunately there is no feedback when you check a box even though a rule is created, so don't be careless. You can actually create multiple loads-after rules all at once for that same plugin, if that ever proves necessary, by simply checking other boxes. When you're done, click the original plugin again- the one with a check in its box.
If you choose to drag-and-drop from the first plugin to another one, the Manage Rules dialog will open with both the fields already populated and a drop-down rule selector in between them. That selector has two choices you'll use 99% of the time: Loads After and Requires (e.g. "loads before").
The drag-and-drop method is most useful if both the plugins are visible in the same view. The Edit-and-checkboxes method is more useful if you need to scroll the view much to locate the other plugin(s).
You could also open the Manage Rules dialog directly. If you do that, you must populate the plugins fields at the bottom by clicking on each one and scrolling through the list of plugins until you find the correct ones, then click into the rule selector and pick the correct rule "direction".