whats the difference between gears?

[SheFly]

...some have shimano tiagro and some have shimano 105,what do they all mean?

Those are the levels of componentry that Shimano uses. Tiagro is the lowest level, then 105, Ultegra and Durace. As you move up levels, the componets get a little "better" - lighter, but also more expensive.

Unfortunately, you're going to have to still work to go up the hills, regardless of the componentry .

SheFly