Summarize this article:

Tap the Google Drive app icon, which resembles a blue, green, and yellow triangle. Tap a folder in which you would like to save your scan. It's in the bottom-right corner of the screen. A pop-up menu will appear. This camera-shaped icon is in the pop-up menu. Your phone's (or tablet's) camera will open. The document should be centered in the middle of the screen. Make sure that your document is flat and completely on-screen before proceeding. It's a blue-and-white circle at the bottom of the screen. This will scan your document. This is in the bottom-right corner of the screen. Doing so saves your scan.  You can also crop your scan by tapping and dragging any of the spheres located around the edge of the scan. For more options (e.g., color), tap ⋮ in the top-right corner of the screen. To add more pages to the PDF, tap + and then scan another item. Tap ⋮ in the bottom-right corner of the scanned document's thumbnail, then tap Download in the resulting pop-up menu.

Summary:
Open Google Drive. Select a folder. Tap ＋. Tap Scan. Point your phone's camera at a document. Tap the "Capture" button. Tap ✓. Save your scanned document onto your phone.