Why can't I adapt the template that I downloaded on Adobe Stock?

This template relies on the Pages panel, and it's complicated for a new user. Here's how to get started:

1. Open the template.
2. File > Save as to save it as as a new name.
3. Window > Pages > Panel menu > View Pages > By Alternate Layout
   
   There are four templates within the one you downloaded. Begin by deciding what paper size and color theme you want. Two sizes (Letter and A4) and the themes (light and dark). Double click the icon for each of the four page 1s to decide which one you want to use. Pick the one you like the best. You can ignore the other columns for now, and eventually delete them so that you don't go to the wrong page later.
4. You will design your CV on the pages 1-3 of your favorite. Let's say you pick the second page one as per my screen shot. Double click that page 1 icon and start adding your information to the body of the document. Use the Type tool (the T) to add, delete and format the text.
   
5. To edit the photo and your personal information, you need to navigate to the Master page behind that Body page, so note the letter that appears on each thumbnail. A for column 1, B for column 2, C for column 3 and D for column 4. Double click the name of the corresponding master page. Now you can update the information at the top of the page. In my screen shot, I'm in the 2nd column and a B appears on each column two thumbnail, so I would double click on B-A4 Master-Light.
6. To return to the Body pages, double click the icon for your page 1. The photo and personal info is updated on all the pages.

To save your sanity, at some point, use the trash can in the bottom right to delete the unnecessary masters and body pages.

~Barb

Some of the elements of the template may be locked on a layer, or may be placed on a master page which require you to edit them there.

If you are totally new to InDesign, I suggest learning a little about InDesign first. Two good sources:

(1) Sandee Cohen's excellent beginner's book is inexpensive and quick to learn with:

InDesign CC: Visual QuickStart Guide (2014 release)

(2) You can get a free 10-day trial on www.Lynda.com and see David Blatner's InDesign Essentials course.

InDesign is more complex than a word processing program, and you can't just use it with templates without learning more about the way it works.