Adword competition bar

Hi there,
i'd like to know if i understand well the competition bar... If the competition bar is low does that means that there would be only a few ads (or none) in relation with my keywords? If there's no advertiser so the ads will be related to something else?
Is that really matter?
And for example if my keyword is "football" and the bar is empty but the bar is full for "football shoes" could i have ads related to football shoes if i made a site on "football"?

If the bar is empty it means that there are no or close to no advertisers for this keywords = no $$$.

And i connot have ads related to my keyword? I suppose the bar is often empty for long tail keyword but it may have a lot of advertiser who advertise for something in relation with that...
And for example if I have a good keyword with an empty competition bar and 2$ cpc, does it means that there's at least one advertiser who pay 2$? In that case should I try or it's really important to have adword competition?

Thx

No competition on keywords can play out different ways.
In my niche there was 0 competition for the keywords I chose, 20k monthly exact match searches. There's now 70% competition for those keywords now that my site is sitting in position 4 on page 1. Sometimes no competition just means there's not any good adsense sites with traffic for anyone to target...so go build it.

No competition can also mean you picked a terrible niche or bad keywords.

Those keywords can still be worth something if you aren't only doing MFA. I look for high searches and low amount of ads all the time, sure there's no advertisers but if I can get them to unlock content they are looking for I'm getting paid.