Call your folder "Site Assets". Set the sharing permissions on the folder to "Public - anyone on the internet can see it". Learn more about visual design.
All images, audio, video, animation, writing and any other assets included in your website must be original work, purchased work, work released under a creative commons license or work for which they obtained expressed written permission for use. Place these assets in your Google Drive folder.
Add the assets that you created into your wireframe layouts as you progress through the asset creation process. Instructions for working with Google Sites can be found on Google's website.
Logomaker.com: free logos if you make an\account... or you can screenshot the logo you create.
Photopea: a web-based image edit that looks and works like Photoshop.
Vectr: a web-based vector drawing and type tool that works like Adobe Illustrator
Google Drawings: Google's free drawing tool