1. Easiest is wireless delivery of paid or free content (e.g. direct from kindle store or by downloading the Project Gutenberg catalogue to the kindle for browsing and direct downloading). Click and text arrives ready to read.
2. Next easiest is to take existing content and converting it to display on kindle as PDF, TXT, image files, or kindle format (azw, azw1, prc, mobi).
3. More steps involved to arrive at final text on kindle is to collect web clippings (select text to excerpt). For users of the Firefox browswer there is Zotero for collecting various web sections for later use. For several operating systems and browsers there is Evernote and its web clipper tool: select chunk of webpage, then right-click to send to this online personal filing cabinet. Then select all the segments saved to Evernote for Export (and putting onto kindle in a big batch).
4. Most time intensive of all is to select >copy >paste to a word processing file and saving as a collection of excerpts.
5. In some cases you can reply on a webcapture program used for offline reading of a webpage and/or selected subordinate webpages linked from the main page. The full version of Adobe Acrobat includes this feature and preserves the hotlink functionality when producing a batch of PDFs from the targeted URL. If the result is mostly text, then kindle does all right with its native PDF viewer. But if the format is cluttered, then it may work better to convert the set of PDF pages into kindle (azw) format instead.
Alternatively, programs like Readability, are designed to streamline a cluttered website for easier text engagement. By filtering out the clutter first, then a webcaptured set of PDF pages can be an effective way to harvest a bunch of writing with the touch of a button (entering the target URL for capturing, along with the number of levels beneath that page for appending to the targeted webpage).