This might be a dumb question,but how do I know which lane a character is best suited for and why does it make a difference in first place?
Not dumb at all! Actually a lot of people are used to just copying other people on lane placement (not that there is anything wrong with that, since you end up placing people in the right places regardless), without really thinking about why. The current meta puts the AP carry at mid, an AD carry and support at bot, a jungler (usually one with a fast clear, or good cc, something that doesn't need too many items, etc.), and something that can survive alright top and makes sense in your team comp (of course if you are playing to win, you will always attempt to synergize your picks).
This happens for many different reasons, but a lot of it begins to make sense when you think about the nature of the champ and their position in regards to map objectives (dragon, buffs, etc.), who needs gold (in an AD and support lane, it is currently very popular to allow the AD to get all the last hits, and to make the support buy items like philo and heart of gold, same for several junglers), just you know general optimization of resources and usage of the champ's skillset. Keep in mind that this is part of a long-going "meta" and is subject to change. In fact, many teams subvert these lane assignments; knowing that another team has picked a "weaker" laning phase top, vlad for example, you may decide to send your AD and support up there. In the past there have been roaming supports, AD mids, etc. Basically, though, people just follow what the pro players are doing at the moment, so if you check that out and think about the decisions they make it'll become clearer to you. Essentially this is what they have decided is the most efficient way to play.
ferrio got dat tl;dr
I mean, it's pretty useful to know how the enemy team comp will adhere to the meta and how you can counter their adherence. For example, when talon was less weak he was played in mid a lot, since his skillset countered popular mids. People started playing manaless APs at top because they had good survivability and could participate in a double WOTA strategy. Counter-jungling became very popular after M5 cleaned house with the strategy, disturbing the timing of teams that didn't ward their jungle or picked junglers that couldn't fight well by themselves in the jungle. Putting a manaless AP in mid can allow you to have a blue reliant jungler. !!! just gotta think about how the champ you pick will do their role efficiently