While you can’t travel to Delft directly by plane, it is a small city sandwiched between Rotterdam and The Hague and is still extremely accessible. You can fly directly to Rotterdam The Hague Airport, and though it’s nearby, to get into the city by public transport you need to get the number 33 bus to Rotterdam and then a 15 minute train. Alternatively you can grab a taxi for €25, which works out as a great deal if you share it with 2-3 others.
More likely you’ll fly into Amsterdam Schiphol Airport, since it can be accessed from anywhere in the world. There’s a direct train into Delft for €9.10 which only takes 40 minutes - pretty convenient.
If you’re travelling by train, again you’re likely to pass through Amsterdam for a connection. This is easy, since services run between the two cities all day, every day.
Delft is not a big city - there are 100,000 people or so, but the city centre itself can easily be navigated by bicycle or on foot if you aren’t in a rush.
It’s the same throughout the Netherlands - people love their bikes. Unless you really enjoy taking buses or walking, I recommend you invest in one as well. Because there’s a large turnover of students every year, people are always buying a bike one year and swapping it for €40-50 the next year when they run out of use for it. Also, because bikes are just so damn popular out here, they are perpetually up for sale.
There are buses that crisscross all over the city, and you can use Check My Bus to find all the times and routes which will help you get around. While you’ll see trams around Delft, they are actually part of The Hague’s network and so aren’t very helpful for navigating Delft itself.
It is extremely rare for locals in Delft to buy single transport tickets. Instead, everyone uses an OV-Chipkaart, a Dutch travelcard which is valid on all public transport across the country. You load it using cash or card at central station. There’s no fixed "ticket price", but rather the intelligent OV-Chipkaart system calculates the length and duration of your journey and charges you accordingly. If you don’t scan your card for a journey you could face a substantial fine, and no excuse will get you out of it!
You can also pay to get 40% discount on all train travel across the Netherlands in addition to your Chipkaart. It costs €50, so if you spend any time travelling in the country (such as to Rotterdam or Amsterdam) then it will pay for itself within a handful of journeys.