Investment Terms and accelerators

Hello All,I am trying to figure how investment and accelerators work. I was looking at techstars.https://ift.tt/3jQrFE9 Equity Investment In Common SharesEquityWe purchase the right to 6% of the company’s Fully Diluted Capital Stock at the Qualified Financing (as defined below) for $20,000 USD. We will be issued our 6% common shares immediately before the Company’s next equity financing of $250,000 USD or more (a “Qualified Financing”). Our 6% equity investment is subject to our Equity Back Guarantee. Here is a helpful post by David Cohen explaining our intent for the Equity Back Guarantee.What does this mean? Do they give you 20k for 6% of company, or this 20k allows them to buy for cheaper price later on 6 percent of the company.What does does "Fully Diluted Capital Stock at the Qualified Financing " means?If you want to be part of accelerator do you have to take their 20k investment or you can be part of accelerator without giving away 6% of the company? see hubwealthy.com/wealthy