I'm going to be using it...I won't say what days because this is not an ad...but I could really use some help from the locals!
Thanks for your help
the Metro system website or app will be your actual time when you need to be somewhere at a precise time. We got a saying around here, you might have heard it in other contexts: YMMV ! 
Once you get used to it, it is great. Except sometimes you will be astounded how far behind it can run. The weekends and late night with a color switch I have been delayed over an hour before. I am not kidding. Most of the time it is very smooth. A car can mean up to $60 a night to park it at a hotel and wasted time and money trying to find parking when you go out. Trains do shut down before midnight every night except Friday and Saturday. Mix it up with shuttles, cabs and Uber and you will be fine.
Study a map first of all. On your mobile you can pull up www.wmata.com and it will tell you when the next train runs from a drop down list of stations or even the next bus nearest you if your location awareness is on. Also on mobile use google maps. It syncs with the Metro system and is a lifesaver. The DC Circulator is also wonderful if you are in DC proper.
I would also recommend using the Curb app that will map and order a taxi for you. Uber is good sparingly but I don't like having a list of hotel addresses on my bill. I have only been in one Taxi that was not sparkling clean, Uber has made the taxi business better for the consumer. Uber and Taxis can have pervy drivers that are a little too interested in you, shut down the small talk quick with those but most are ok.
We don't have a system like this where I am from and I learned it quickly. It is so carefree and planet friendly to roam around carless. Have fun, the weather is perfect for this.
They are sold in machines at every Metro station; they cost $ 10, but carry $ 8 in usable fare. You could use the paper farecards but Metro is charging a $ 1 for every trip using the paper card, so in one round trip the Smartrip card pays for itself, and then you are saving $ 1 every time you ride. When you go through a fare gate the gate will tell you how much the balance is on the card, and you can add to it using machines at each station, with either cash or a credit card. The card can also be used to board buses in both the Metrobus and other jurisdictions' bus systems (in VA, that includes the Arlington, Alexandria & Fairfax bus systems). Plus, when you transfer from a Metrobus (or other bus) to the rail systems (or vice versa) you get a discounted fare on the second conveyance. If you lived here, you could also go to the WMATA website & register the card & set it up for automatic replenishment (for example, I have mine set up so that whenever I go through a fare gate & the balance goes below $ 10, the system will add $ 20 from a credit card account AND send me an e-mail notification each time it happens. Also, once it is registered, if your card is lost or stolen, you can call a Metro phone no. with the card number & the system will freeze the card balance so it can't be used, plus you can get the balance remaining transferred to a new card (so be sure to record the card number, along with the phone number, in a place you can quickly retrieve it).
Echoing what others have said, the system is far from perfect & you can expect occasional delays & sometimes long waits for trains, especially late at night & most weekends when serious maintenance is performed (sometimes resulting in a number of stations being closed for the weekend). But it is by far the easiest & cheapest way to get around, particularly downtown. On a business day, well over 700,000 riders are carried, so it gets many folks to & from their jobs every day.
The other thing to look into are the several Circulator bus routes that can get you to & from places not well supported by Metro, like Georgetown, and only cost $ 1 per trip.
Good luck, & enjoy your visit!
ot Perfect 2) The easiest way to get around. The problems that are being addressed and fixed go way back. The second busiest subway in the country and the boards and General Managers over the years thought maintenance wasn't necessary. I sure hope they learned their lesson.
I'm pretty sure DC's Metro is the only major urban transit system that is dependent on three separate governments for funding (4 if you count the Federal Government) and has never had a reliable long-term funding program, dependent on annual appropriations approved by the political 'leaders' in DC, Maryland & Virginia, plus whatever the US Congress kicks in through USDOT funding. Thus it has difficulty making long-range plans, never being sure what funding will be available. As a result, they have historically been underfunded for years; management usually chose to fund operations at the expense of maintenance. Of course you can only do that for so long, & eventually the new wears off & stuff begins to break down. So they are now caught in a catch-up mode while still having to move 700K + riders every weekday. Metro management has for years implored the supporting jurisdictions to establish a stable long term funding stream that they can plan around. Unfortunately, VA is pretty conservative, MD a bit on the liberal end of he spectrum, & DC is extremely liberal, so getting these three entities to agree (on anything) is very difficult. So it will likely be a long & very gradual path to m ore reliable service.