It is a little questions

[Abcslasher]

1)Can you explain me for what honor is used?
2) Now i have 300 herbalism and 300 tailoring, wanna change to aclhemy. What way better : make herb+ alchemy or twink with alchemy + another?
3) what profession brings more gold : Blacksmithing or Leatherworking?

[Tinkertown]

I like your nick. It fits.

1) Honor isn't a currency. The amount of honor you farm compared to others determine how much your PvP rank goes up or down during the weekly calculation around noon servertime on wednesdays.

2) Always be engineer. Other than that it doesn't really matter.

3) Neither. Really. I'd bet the vast, vast majority of people with 300 in either never make the leveling cost back.

[am0n]

1.) As Tinker noted, Honor is just another experience bar for PvP rank. However, that experience bar varies each week, based on participation.
2.) If you absolutely want to go Alchemy, I'd probably recommend keeping Herbalism. You are likely to just purchase low-level herbs, but the higher level ones get costly and it'd probably make more sense to farm those yourself.
3.) As Tinker mentioned, most people don't make back the money, because just about every guild has one or two people doing each trade and they are likely to go to that person to get stuff done for them. If you are in a guild that has a need for either of those professions, or a specialization in one of those, discuss with them whether you should take up that skill and what kind of support/need the guild has for it. However, there are some BoP items that each profession can craft, so if those items are something you absolutely want, working on the skill may make sense.