Resources

The fields
You can access your fields overview by clicking the first circle up inthe Travian screen. If you take a look around you will see the hourly resource production, your troops (none, probably), and 4 kinds of resource fields:

Resource kind	Appearance	Notes
Wood/Lumber		The Teutons as a tribe has troops of which training requires a lot of wood. The residence as a building costs a lot of wood to upgrade.
Clay		Clay is the primary resource for the Gallic tribe, which has very clay-expensive troops. Also, an actively developing village needs relatively more clay.
Iron		This previous resource is mainly used in the expensive armour of the Roman troops and walls. Because of this, Romans will always be hungry for Iron.
Crop		The most troubling of the four resources. Buildings cost less crop than the other resources and you have 6 croplands instead of 4 fields, but you still do not have enough. This is because the crop production is lowered everytime you upgrade buildings/fields or train troops..

To upgrade a field, click the image of it and click the 'upgrade to level X' link. If this link is inactive, it should display the reason why.

Try keeping your resource productions as equal as possible, with crop at 50%. For example:
Lumber: 100/hour
Clay: 100/hour
Iron: 100/hour
Crop: 50/hour
Of course you have to adapt your resource production to your needs, this is just a general rule.

Storage - - Granary and Warehouse
The granary and warehouse store produced resources for later use. The warehouse stores Lumber, Clay and Iron where the Granary stores only Crop. Later in the game these buildings cannot be missed, and they are also prerequisites for buildings like the marketplace. In the endgame, the Great Granary and the Great warehouse also become available to builders of a Wonder of the World.

Secondary Industries - - sawmill, Brickyard, Iron foundry, grain mill and Bakery
The secondary industries are buildings giving a bonus on the resource production of a certain kind of field. Each resource has its own secondary industry, and Crop even has a tertiary industry.

• Lumber: The sawmill saws all the rough wood coming from the woodcutters increasing the production with a maximum of 25%. Requires a level 10 woodcutter.
• Clay: The Brickyard processes all clay to bricks, increasing the production with a maximum of 25%. Requires a level 10 Claypit.
• Iron: The Iron foundry makes iron blocks out of the rough iron ore from the mines, increasing the production with a maximum of 25%. Requires a level 10 Iron mine.
• Crop: The grain mill processes the raw crops to grain, increasing your production with up to 25%. This requires a level 5 crop field. When you have upgraded to level 5 and have a level 10 cropfield, you can build the Bakery, which adds another 25%.

Advanced storage - - Great Granary and Great warehouse
As the game moves on you might want to store more resources and still have some building spaces left. This is the most needed in the Wonder of the World villages, which is why you can build the Great Granary and Great warehouse there. Storing four times as much resources they can save you a lot of building spaces and upgrade time.