Here are some more detailed steps to get you a better start.
First, upload your custom images to media library and then add them inside links inside a text widget.
You can add the text widget to the first footer area. Once it's showing up on the page, right-click on the widget area and select the "Inspect Element" option. That should pull at the HTML for what you click done as well as all of the CSS that applies to it. You will need to find the "ID" attribute for the text widget that you added. It will be something like "text-33" only your ID value will be something other than 33.
To reposition that element, you can use some CSS like this:
Replace YOUR_TEXT_WIDGET_ID with the id value for the text widget where you added your social media icons.
You will need to adjust the "top" and "left" values to position the icons where you want them. Also note that if you had some icons you may need to add a width value to the block.