Detailed instructions are [here](https://support.google.com/docs/answer/97447?co=GENIE.Platform%3DDesktop&hl=en), from which the basics are:

> **Add an image**  
> 
> - Open a document, spreadsheet, or presentation in Google Docs, Sheets, or Slides.
> - Click Insert and then Image.
> - Select from the following options:
>     - Upload: Choose an image from your computer and click Open.
>     - Take a snapshot: Use your webcam and click Take a snapshot.
>     - By URL: Paste the URL of an image from the web and click Select.
>     - Your albums: Choose an image from one of your photos albums stored on the web and click Select.
>     - Google Drive: Choose an image stored in Google Drive and click Select.
>     - Search: Choose an image from the stock photography archive, or the Google and Life archives, and click Select.
> Your image will be added to your file.
> 
> **Image size and format requirements**
> 
> Images must be less than 50 MB and be one of the following file types:
> 
> .gif
> .jpg
> .png
> 

There is also a [video](https://www.youtube.com/watch?v=6WFdT2SX7QU).