(I assume you have a nostr account, if not follow an Idiot's Guide to Joining Nostr written by someone who is less of an idiot).
Step 1:
find the RSS feeds you want to follow
(Right click on the website's page, and choose Page Source. In the new window that appears, use the “find” feature and search 'rss')
some websites will have a standard format eg. substack add '/feed' at the end of the URL.
Step 2:
Add at least one of the following relays to your nostr account to read the feeds:
wss://nostr.data.haus
wss://relayable.org
wss://relay.highlighter.com
Step 3:
add your RSS feed URLs to atomstr
(you can also 'find' existing feeds people have already added to atmostr)
Step 4:
open the link to the generated RSS nostr accounts in Nostrudel and Follow
Step 5:
Clicking on Follow in Nostrudel also brings up Lists you have created to sort your RSS feeds
or select New List to make a ..new list
DONE
(these lists will also show up on other clients eg Amethyst, will show up on homescreen clicking on All Follows dropdown)