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.
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 but if you do not live in the US, India or the UAE, then you will not find your currency on there.
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.