The first step in the process of scanlating any manga is obtaining the raws. The first step is to download the file the raws are in, then the second step is to extract the raws from this file.
Raws can often be found on piracy websites dedicated to hosting them (none are listed here to avoid link rot, but they can be found on the Internet). Be aware that some websites will add watermarks; since it is best practice to not keep watermarks from these sites (the only kind of acceptable watermark is an author watermark), one will either have to manually clean them or find a different source.
Useful tools
There are some general-purpose manga downloading tools; a notable one is HakuNeko. Alex's Raw Downloader is really simple to use for sites that it's compatible with (click "Info" on the site for a full list of compatible sites).
Websites that allow online viewing of manga will often render the images in a <canvas> element, which can then be extracted with browser extensions like Canvas Downloader for Chrome, ImageAssistant for Chrome or Image Picka for Firefox. Be aware that resampling may occur. Some websites like Bookwalker add a near-invisible barcode at the bottom that points to your account; one should take care to remove the 3 bottom pixels of all pages.
A useful tool is this Stack Overflow answer which provides a script/bookmarklet that re-enables the ability to right-click on websites that have disabled it.
Screenshotting
Usually an easy way, but can be low quality due to the resampling that may occur, and is labor-intensive.
PDF
PDF raws are most common when obtaining self-published raws from websites such as https://booth.pm/en
Most raw PDFs are single pages with the images embedded in each page. So the next step is to extract the images that are embedded. There are two tools that are often used.
Click the "Start" button Successful Kindle archive extraction
The file will be extracted to the output directory. It will have several directories, but within at least one somewhere there will be an image directory with the extracted images. One possible location, the images may be elsewhere within the directory structure depending on the type of archive, and how it was put together.
Bookwalker
This requires downloading a modified Chromium executable on a Windows computer and the ability to run a PowerShell command.
Warning: The Chromium client downloaded here bypasses safety features and should not be used for anything other than downloading manga from Bookwalker.
These instructions apply to the latest version at the time of writing, version 0.3.3:
Bookwalker window sized for downloadingBuy the manga on Bookwalker. For most Japanese releases, you will need to use the Japanese site, not the global site.
Open a powsershell or cmd in the unzipped browser dir:
Navigate to the unzipped directory in explorer.
Shift + right-click in the folder.
Select "Open PowerShell window here".
Open the browser with command line: .\chrome.exe --user-data-dir=c:\bw-downloader-profile --no-sandbox
Log into you Bookwalker account in the launched Chromium window.
Open the book you want to rip in the viewer.
Adjust the window so exactly one page is visible.
If you can get the script to automatically click (step 6 here), that's good, but it is not working at the time of writing due to Bookwalker code changes.
Instead, you can just click through the manga you are ripping, one page at a time (giving each page enough time to load).
After you've clicked through all the pages you want to rip, the pages will be in C:\bw_export_data under a folder with a name matching the ID in the Bookwalker URL.
Creating a shortcut
Creating a shortcut for Bookwalker downloader Chromium
To create a shortcut that launches the modified Chromium application with the appropriate permissions:
Right-click on chrome.exe and select "Create shortcut".
Right-click on the new shortcut and select "Properties".
Select "Target" and move the cursor to the end.
Paste --user-data-dir=c:\bw-downloader-profile --no-sandbox (including the space before)
The new "Target" should look like C:\path\to\Chrome-bin\chrome.exe --user-data-dir=c:\bw-downloader-profile --no-sandbox.