And so on and so on. The point of this step isn't to come up with your final list of keyword phrases -- you just want to end up with a brain dump of phrases you think potential customers might use to search for content related to that particular topic bucket. We'll narrow the lists down later in the process so you don't have something too unwieldy.
I use Ahrefs to find ideas for keywords to add into content, and content to create around keyword opportunities. I like how Ahrefs shows keyword difficulty, search volume, traffic potential (how much organic search traffic it’s possible to get when you rank #1 for a parent topic keyword) and lets you group keywords together to create lists. It’s really useful.
6. Filters. On the top area of the main pane, you can find the “Filters”. These will allow you to filter your keyword suggestions list in real time. Just start typing and your list will be filtered accordingly. You can filter for “Keywords” (to only show keywords that include a specific word or words); “Suggested Bid” & “Local Searches” allow you to enter minimum or maximum values; “Advertiser Competition” (this comes in handy, because the higher the competition the more money there is to be made if you target that keyword); “Avg. Amazon Reviews” (a neat feature for those who sell products on Amazon or have an Amazon FBA business — less reviews equal less competition, hence more chances to rank on top of Amazon’s product search pages); “Avg. Keyword Competitiveness” or “KC” is Long Tail Pro’s proprietary metric that calculates how hard it is to rank for a keyword in a range from 0 to 100 — 0 being no competition and 100 impossible to rank for. All of these filter columns can be used to sort the keyword suggestion list as you prefer.
WordStream for PPC is a full-service PPC management platform for creating, optimizing and managing pay-per-click advertising campaigns in Google AdWords. Our PPC software includes easy-to-use PPC keyword tools, campaign creation and expansion tools, Quality Score optimization tools, and more to help marketers get their PPC work done quickly and cost-effectively. WordStream for PPC customers experience increased traffic and greater ROI.
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input.  In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).