You'll want one Tracker per distinct campaign or topic you want to track and each Tracker can include up to 15 search queries for that campaign. A search query can consist of multiple terms or keywords. Each Tracker can also include up to 5 exclusion terms. 

Here's an example to clarify. Let's say you want to monitor all the tweets about your client's product launch. Your client's name is Acme Company and the new product is called AcmeX. They also have a Twitter handle, @acmeco. The problem is that there's another company called Acme that makes bread and you do not want to find tweets about Acme bread. So, we'd want to track any tweet that mentioned the company, the product, or the Twitter handle, but not mentions of the bread company. Here's what we might search for in a Tracker:

This Tracker will find any tweet that mentions any of the search queries (a tweet only has to match one line to be found, not all lines). It will exclude all tweets that include one of our search terms but also includes the word "bread". 

We left off the @ before the Twitter handle to be sure we found mentions, retweets, replies, as well as tweets posted by the @acmeco account. There's more info about searching for tweets from/about Twitter accounts here.