Which items should I buy (or not) in Arena

Edit: This answer is no longer correct, but it's here for historical reasons. Apparently now Mages do Magical damage with their auto attacks as well. See this answer: https://gaming.stackexchange.com/a/126776/1721.

All basic attacks do physical damage. That's what balances Physical and Magical gods. Magical damage gods do a lot of damage with their skills, but their basic attacks are weak. Physical damage gods have strong basic attacks, but weaker skills. (Some of them have strong skills, but those ones have melee autoattacks so they're not overpowered.)

You can tell what type of damage a skill does by looking at its description.

There are two things you have to look at, what type of damage an ability does and what stat it scales with. In the above picture you can see the line Damage: Magical. That means that ability does Magical Damage, which in-turn means an enemies protection against this skill would depend on their Magical Protection stat.

Then look at the Damage per hit line. The numbers in green are the base amount of damage that skill does at each level of its evolution, in this picture, the skill does 100 base damage per hit when it is level 1, and 180 base damage per hit when it is level 5. Then look in the parenthesis next to it and it will tell you that that ability does an addition amount of damage per hit that is equal to 70% of your Magical Power.

The second line, the one in the parenthesis tells you what stat that ability scales with, so if you want that ability to be strong, you have to increase the correct stat.

In Conquest, there are three lanes: middle, long, and short. The two outside lanes have a different distance between the middle towers, which is how you can tell them apart. Unlike other MOBAs, they aren't always on the same side of the minimap. Depending on which side of the map you start on, long could be either left or right; the minimap will rotate so that your starting base is always at the bottom and the enemy base is at the top.

The roles in a game of Smite, as far as the metagame is concerned, give information about what your goal in game is, and where you should be playing. These loosely correspond to the god type.

Here's some information about how each role should treat the early-mid game to get you started.

ADC: Pretty much always a Hunter, this player starts the game by taking the attack speed buff (purple), then goes to the long lane and farms. He stays in the long lane, farming, and grabbing the attack speed buff whenever it respawns. He will also go with his team for early-mid game gold fury objectives, since that helps his farm.

Support: Usually a Guardian, although some others work as well. This player starts by helping his mid and ADC get their buffs, then hangs out in the long lane with the ADC for a little while before roaming mid and taking some of the jungle camps. The support will help gank for the ADC and mid, but generally doesn't cross mid into the other side of the map.

Mid: Usually Mages will play mid, although there is a little variation. The mid takes the attack damage buff (red), then goes to the mid lane. This player can shove his lane (kill all the minions quickly) and then go to either long or short as a "rotation" to help the players there and get some kills. If you can shove your lane harder than your opponent (or outright kill your lane opponent), you can get an advantage.

Jungle: You will usually find assassins in the jungle. The jungler starts by taking the speed buff (yellow), then helping the solo laner take the mana buff and going to short with the solo laner for a few waves. Then the jungler goes into the jungle and kills neutral camps, and helps to gank all three lanes.

Solo: The solo laner can be any god type, so long as they have decent sustain (the ability to stay out of base for a long time, usually through healing) and skirmishing (basic 1v1 combat ability). Warriors are usually a good fit, although there are characters in any role that can play solo. The goal here is to farm. You're generally going to be alone for most of the early-mid game, with your solo enemy, facing each other down and farming.