The meaning of the three kinds of penetration

The formula for calculating the effective armor rating in world of tanks is:

Armor tickness/cos(impact angle)

With an Angle of > 70% always leading to a ricochet, this leads to this table:

Impact Angle    Effective Armour Thickness
    0°                 100%
   10°                 101.54%
   20°                 106.42%
   30°                 115.47%
   40°                 130.54%
   50°                 155.57%
   60°                 200%
   70°                 292.38%
  > 70°                Ricochet

(source: world of tanks effective armor rating)

Which angle to chose depends a lot on the tank you're driving and how it is armored. But in general, having at least a slight angel towards your opponent is a good idea.

For example, if you're driving a tank with 100mm front armor and 80mm side armor, a 45% angle on both front armor would give you an effective front armor of 141mm and effective side armor of 113mm. In this example having the opponent hit your side at an angle would still give a lower chance of penetration than hitting the front armor at a straight angle.

However if the situation is the same, but the tank you're driving only has 60mm side armor this means the effective rating of the side armor would be 85mm, which means you're giving your opponent an opportunity at an easier penetration, in this case it would be still good to present yourself at an angle, but less than 45%. (a 30% angle in this case would give you 115mm front armor and 120mm side armor)

Lower tier tanks will only play on a limited subset of maps, to give players the chance to familiarize themselves with them quickly.

Battle Tiers 1 and 2 fight on these maps:

• Malinovka
• Himmelsdorf
• Mines
• Province

Battle Tier 3 additionally fights on these maps:

• Karelia
• Prokhorovka
• Ensk

The province map is not available for Tier 4 and above. For Tier 4 and above the map picked should be random, but in practice this is not the case. The reasons behind this are not completely clear, although wargaming does seem to give new maps a higher chance of appearing.

See this forum thread on map distribution stats for more information on the actual frequency of appearance of some maps.