If you walk into a dealer and ask for a valuation, the dealer will glance quickly through your collection and offer you what he (or she) is prepared to pay, up front, for it. This will normally be less than it's "true value"; the dealer will later be trying to sell your coins for more than what he paid you for them - that's how they earn a crust. The dealer will also have time later to go through your collection more carefully, looking for scarce dates and types.
If all you want is quick cash for your coins with minimal fuss and effort on your part, this is the best way to go. Only don't be afraid to shop around; take the collection to various different dealers for valuations.
Selling on
ebay or some such similar online auction site normally gets you better prices, but its more effort on your part - you have to take pics, pay listing fees, mail out the right coins to the winning bidders, etc.. It can take quite a fair chunk of time to sell off an entire collection in this way.
Most dealers are happy to sit down and itemise the value of each and every coin in a collection (normally this is done for insurance purposes) but doing this takes time, and the dealer isn't a volunteer charity worker; time is money, so they'll charge an hourly rate for his service. Since at this stage you're intending to sell, this would probably be a waste of money, though it could in the end be worthwhile by giving you an idea of the "true market value" if you choose to sell your coins individually on
ebay.
We here on the forum are in effect "volunteers", and we'll happily look up any coins you post pictures of (or describe adequately), and let you know if there are any scarce dates or valuable types in there. If you're thinking of selling them on
ebay, you'll need nice clear pictures of your coins anyway. Simply find the part of the forum that's most relevant to the coin you're asking about (for example, ask about Australian coins in the
Australian section), and post the question there.
Be warned: scientific tests have proved that coin collecting can be habit-forming. The more you learn about your coins, the more inclined you'll become to keep them rather than sell them.

Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis