So I'm a level 10 lancer...

[Niwashi]

can someone explain the whole class thing that happens at lvl 10

Once you reach level 10 in your first class, you have the option of adding others. To do so, go to the guild of the class you want to join and talk first to the guild receptionist to pick up a quest which will then have you talk to the guildmaster. That will unlock the class and give you a starting weapon or tool for that class. After that, you can change classes simply by changing your equipped weapon/tool.

There's no limit on how many classes you can join, or how far you advance in each, but you have to advance each one seperately. Your level as a lancer would not carry over to your level as an archer, for example. You start each new class at level 1. There are 8 adventuring classes in the game, and 11 crafting or gathering classes, so you can have up to 19 different classes on one character and alternate between them just by changing equipment. As you do so, your level also changes each time to the level you've reached in that particular class.

As a lancer, you'll have started off in Gridania. The other adventuring guilds in Gridania are the Archers' guild and the Conjurers' guild. It's also the home city for the Leatherworkers, Carpenters, and Botanists guilds if you want to move into crafting. Once you get to other cities (probably around level 15 or so) you'll find guilds for other classes.

what are free companies or just companies in general are they guilds?

Free companies (sometimes abbreviated as FC) are groups of players who game together. It's the sort of groups which are called guilds in some other games, but due to this game's use of the word "guild" pertaining to different classes, it can sometimes get confusing when players start refering to their FC as their "guild".

Grand Companies are factions within each of the three starting cities. You'll need to join up with one of them I think it's around level 20 or so. I haven't yet, so can't go into much detail, except I know that you earn tokens for your GC while adventuring, and you can exchange those to get special items or unlock various features of the game.

Can you use a scythe as a weapon?

No, it's an off-hand tool for a botanist. It's used for gathering items from Lush Vegetation nodes.

[Niwashi]

You start each new class at level 1.

This fact also means that while leveling up your first class, don't get rid of your starting gear. When you add a new class, you'll need level 1 gear again. All gear not equipable by your new class and level is automatically unequipped. (Each starting city has an NPC who sells duplicates of each race's starting gear, so if you've already gotten rid of yours and don't have any level 1 gear, pick up replacements before going to join a new class guild.)

In fact, at each level range, as you out-level your previous gear, consider whether another of your classes may want the same gear soon. Try to only get rid of obsolete gear when you've outleveled it on every class it's suited for.