The difference between the filter and search engine is the filter will filter down the results displayed within Prospects, Candidates, and Clients. The Search will search through all of the categories.
Within the Contacts section; prospect, candidate, and client tabs hold information that can be quickly found by sorting (or filtering) through the following options: account manager, Independent rep, state, city and company. This can be extremely beneficial for example; when looking for a specific account manager's records and knowing exactly how many companies they are within.
You can access the filter from any of the tabs, just recognize it will only filter out the information from the tab you are in:
The search engine is very powerful, it will search the entire contacts database based upon your search criteria. Choose what you wish to search by in the drop down and begin to type your results. Results will automatically begin to display as you type them.
A great tip when searching is to use as few characters to find your results as possible. Beginning with a more general search and narrowing it down as you input more characters is the most effective way to use this feature.