Don't be overwhelmed by the many different metal detectors out there. I have been metal detecting for over 20 years and have owned or tested many entry level to very expensive detectors. I have learned that most people getting into metal detecting will do just fine with an affortable machine.
It is true that the more expensive machines have more features and can go deeper. This can be helpful for very specific types of detecting, for example looking for gold nuggets. You want a metal detector built specifically for gold nugget hunting. However, the extra depth and features can cost a lot of money while only providing a small benefit.
Rather than wasting a lot of money on un-needed features, I recommend that someone new to the hobby, starts with an affordable setup and then grow into a more advanced one if needed.
The ACE 250 metal detector provides some helpful features for ignoring certain types of items. It is easy to use and you you get a lot for the price. One or two good finds and it can pay for itself. It will find coins, jewelry and other valuables.Garrett Ace 250 Price
I bent too many of the cheap hand trowels that you find at the hardware store. They aren't cut out of metal detecting. It may be tempting to go cheap, but you will end up buying a lot of them. I recommend doing it right the first time and getting a sturdy hand shovel. The Lesche Digging Tool is what most people end up with after breaking lots of cheapos.Lesche Digger Price
Not an absolute must, but it is nice to block out outside noise as some metal detector sounds can be soft. They also, help you not annoy other people at the park with the loud beeps. Some of the expensive options are nice, but not worth the price when starting out. Most metal detectors take the larger headphone plug. For these I like to use an inexpensive adapter along with my normal earbuds when the day is hot. Otherwise, I like to use the Koss UR29 Headphones. They block out a lot of noise, and give a nice sound. Almost as good of sound as the $100 dollar ones that I have tried.Koss UR29 Price
This is not a mandatory item, but it speeds up the process of finding things and just makes things so much easier, that I personally consider it a must have tool if the budget allows. Avoid the cheap ones, though as their depth and performance is awful. From what I have seen the Garrett Pro-Pointer is the most popular one, and is one that I like to use. There are more expensive ones, but the Garrett is tuff, and works well.Garrett Pro-pointer Price
You need something to put stuff in, but a cheap tool pouch or any puch that can hang from your belt is fine. No need to spend a lot of money on a metal detecting branded pouch, some of which are actually poorly made. I learned this the hard way.Dickies Pouch Price
The items about are what most people will need to get started metal detecting. Dealers sell a lot of other items, but most are not needed or are overkill. Try the above setup and expand your equipment when needed, if at all. As for learning to metal detect, Metal Detecting: A Beginner's Guide: to Mastering the Greatest Hobby In the World is a good book, if you prefer books, but detecting is not complicated and you can learn everything you need to online for free in forums and on Youtube. However, keep in mind that on the forums there are a lot of people who spend more money on things than they need to. Some try to convince everyone else to do the same. Beware of these people. The two main areas where more specialized metal detectors really matter is gold prospecting and water proof metal detectors for beach hunting.