Yes, it’s an understatement to say Photoshop is complicated. However, regarding performing restoration with Photoshop I have an excellent book to recommend that helps cut the elephant down to bite-sized pieces.
Katrin Eismann, Photoshop Restoration & Retouching
The chapter list (from the 3rd edition) shows the range of topics covered;
1 Photoshop Essentials
2 Improving tone and Contrast
3 Exposure Correction
4 Working with color
5 Dust, Mold, and Texture removal
6 Damage control and Repair
7 Rebuilding and Re-creating Images
8 Refining and Polishing the Image
9 Portrait Retouching
10 Glamour Retouching
This book takes the guesswork and inefficiency out of trial-and-error learning and explains the specific commands/procedures involved in performing each of these operations.
https://www.katrin-eismann.com/Book description from an ebay listing;
Product Information
Using clear, step-by-step instructions and professional examples, authors Katrin Eismann and co-authors Wayne Palmer and Dennis Dunbar, present powerful tools and techniques in Adobe Photoshop CC for photography and design students. With new example images, illustrations, and techniques throughout, students will learn to transform faded, damaged photographs into beautiful images that are as clear and crisp as the day they were taken, and how to turn casual snapshots and studio portraits into the most flattering images possible. Full-colour, step-by-step examples show you how to: Correct extreme exposure errors and improve colour, contrast, and tone Rescue heirloom originals suffering from mold damage, cracks, and torn edges-even replace missing image information Remove dust and scratches quickly and easily Transform your photos into beautiful, original works of art by converting them to black-and white or tinted images Use a variety of sharpening techniques and tonal-correction tools to add life and sparkle to digital photos Enhance portraits by removing blemishes, reducing wrinkles, and enhancing eyes, lips, and hair, while maintaining the subject's essential character Apply the secrets that the top retouchers in the glamour and beauty industry use to perfect skin, make-up, and hair Retouch and enhance architectural, product and food shots.
Armed with this reference I would not be afraid to wade into Photoshop, as it narrows the enormous Photoshop command structure down to the commands necessary to perform restoration and retouching.