Missing button to create key frame

You have hidden a column in the Timeline. The first thing to do is double-click the Workspace you are using in the Tool Bar and select to reset it to the default. I suggest that you use the Default workspace to start. If all the columns don't appear in the timeline, right-click at the top of the timeline and select the columns you want to see. 

You should also become familiar with the Switches / Modes / In-Out Duration icons at the bottom left corner of the timeline and learn how to use Shift + F4 to show and hide the Parent/Link column.

It will also help you a lot start a new project and open the Learn workspace. This will lead you through the basics of the UI in about 10 minutes. You should also start out with the User Guide or the tutorials on the Home Screen for After Effects. Do not rely on a search for YouTube tutorials because most of the newer ones are presented by enthusiasts and they often contain poor or unworkable workflows and inadequate instructions. Make sure you vet your trainers and make sure that they know what they are talking about. 

If you ever have trouble with a tutorial, post a link so we can help you. You should also share screenshots showing the modified properties of layers that are giving you problems. You can find all modified properties on a layer by selecting the layer and pressing the 'u' key twice. Please embed them and give is a good description of your workflow.

*The Drag & Drop here..." area is buggy and should not be used to share images. Please use the toolbar or just drag your images to the reply field.

Hi Malinda5FBA,

Welcome to the Community and sorry for your issue.

Which property are you trying to animate? Could you share a screenshot that shows the missing stopwatch icon? Also, what's the exact version of After Effects you're using: https://community.adobe.com/t5/after-effects/faq-how-to-find-the-exact-version-of-after-effects-you-re-using/td-p/9972137 

As basic maintenance try resetting the preferences of After Effects: https://community.adobe.com/t5/after-effects/faq-how-to-reset-trash-preferences-in-after-effects/td-p/10634342 

Let us know, how it goes.

Thanks,

Nishu