There are usually three match types. They are exact, phrase and broad.
Exact match means that your ad won't show, unless the search query is 100% exact. So if bidding on "stop bicycle theft" the ad will only show if the search query is identical.
Phrase match means that your ad will show if any part of the search query matches the keywords you're bidding on. So as in the previous example, if you're bidding on "stop bicycle theft" your ad will show for that search query, but will also show for "stop bicycle" or "bicycle theft" queries.
Broad match means that your ad will show if any of the words match. So if we are bidding on "stop bicycle theft" any of the words "stop" "bicycle "theft" will cause your ad to show.
I usually start with exact match. I find that in general, it converts the best. I can be sure my ad is exactly what the searcher was looking for.
Occasionally broad match can work wonders. For example, there's a bank (yes a real online bank) named after a fruit. They have an affiliate program for a credit card. I bid broad on the fruit name, knowing my ad would come up for both the fruit and the bank.
Since the ad is for a credit card, people looking for the fruit didn't click on it. But people looking for a credit card from that bank clicked on the ad all the time. And it had no competition for a very long time.
We must have perseverance and, above all, confidence in ourselves. We must believe we are gifted for something and that this thing must be attained.