Helpful links for Bookings
In this section, you can find some sites that I recommend for booking your journey. For flights, for trains and for metro/intra-city rail. Once again, these companies are not sponsoring me to advertise them.
To book flights around the world, I highly recommend Skyscanner! They are free, ad-free and easy to use. Skyscanner also helps out with hotels and car-hire, but they are not the best option for that.
For planning train journeys in the UK and Europe, I recommend Trainline. They are reliable and very easy to use. You can set your currency and region, look for tickets, book them, and off you go! It's that simple!
MakeMyTrip is better for booking small length journeys and domestic flights. Once again, you can set your currency as you can in Skyscanner.
For metro rail, look for that metro's website (for example Delhi Metro has it's own website) or the operating company's website (for example you plan London Underground journeys using the TFL website as London Underground doesn't have one of it's own)
A small note: I have included some of the booking/ planning platforms in that system's description earlier in the website.
For airlines, you may want to look at the airline's own website (for example Emirates, Qatar Airways, Etihad and more all have their own websites for you to book on).
The same applies for long-length heavy rail - you can use the operating companies websites (or in Japan's case the separate website dedicated to the Shinkansen) to book your train journeys.