In Tanktastic, tanks are unlocked by reaching the appropriate level, then purchased with either silver (normal currency, earned in matches) or gold (premium currency) which is bought with real currency, earned by watching ads, daily rewards, and earned by leveling up.
Here is a list of good starter tanks:
...etc. Most of these tanks do not cost very much but it might take a little time to scrape up enough coins. Be patient.
Tips for using Beginner tanks
Since your tank will be pretty much stock, you will have to play as a support tank. Once you upgrade it you can (only with some of them) move up to an attacking tank. As a rule of thumb, If you like the tank you got, and you use it often, invest a little in upgrades before you buy another tank. Being able to earn more gold with what you got can be even more valueable than just buying the next tank.
T92 Light (Starter tank for US players)- The T92 is a very versatile vehicle for its level. Unlike most of all the other starter vehicles the T92 trades armor for speed and gun performance. Despite having weak armor the T92 has a fast reloading and high damage gun which left unchecked can inflict massive damage, combined with this is the high speed and low silhouette which allows for stealthy gameplay. Finally, unlike all the other starter tanks the T92 can enter level 30+ matches and can still out perform most other players if used correctly.
M26 Pershing - The M26 is a deathtrap at stock level and is best to quickly grind past it as it leads to the M48 Patton, but once maxed out it can become a more dangerous tank using it's mobility to perform the fearsome "circle of death". Make no mistake, the M26 is not capable of fighting it out in a face-to-face match with any other vehicle in the game. But, learn to use the fairly high top speed to your advantage, and the M26 can be effective in low-level matches. The max level is 8.
M48 Patton - The M48 is a good tank, Which combines heavy armor, speed, and heavy firepower and the M48 is HEAT-compatible and so damage is effectively doubled. The M48 is an excellent tank for defending the flag in CTF matches, and for forming part of the main battle line in an assault on an enemy base.
Centurion - Maxes out at level 18, which is one point higher than the M48. Damage is "good" for a low-level tank; unfortunately, the Centurion fires only AP and HE ammunition, so in spite of a maximum damage rating of 94, it actually does less damage than an M48 firing HEAT. The Centurion is a well-balanced tank overall, that doesn't do any one thing outstandingly well but does everything at least fairly well.
FV 214 Conqueror - Fires only AP, APDS, and HE. Heavy armor and good HP for tank at its level, but low top speed and poor agility. Use the Conqueror as a support unit.
T-54 - When stock it has decent armor, damage, and speed, but it has slow turret rotation even after upgrades. Still, don't take the T-54 for granted; it can do a fair amount of damage relatively quick, and has enough armor and HP to absorb a fair amount of hits as well.
Type 59 - A basic tank, with statistics somewhat similar to the M48. It's faster than the Patton but has a lower damage stat and limited shell choices. It can only fire AP and APDS rounds. Fully upgraded, it has higher armor stats than the M48.
Type 60 - A small, double barreled, Japanese tank destroyer. It's fast, as expected, but limited barrel movement and poor damage makes it vulnerable on the run.
Spahpanzer Sp I.C. - Fast, heavily armed, lightly armored. Spawn, kill, die, repeat. It can one shot most tanks in its tier and reload very quickly, making it a dangerous opponent for light/medium tanks.
Type 61 - High amount of damage for tank's level. Fires only AP and HE, but firepower is still heavy enough to do 100+ damage to most low-level tanks. Otherwise, it's an overall bad tank and rarely ever seen in low level matches.
T95 Medium - A very useful tank to have. Damage is light, and the T95 only fires AP and APDS, but the high speed and good armor help make up for the light firepower. Speed maxes out at 50kph+, making the T95 an effective flag-running tank. Make use of the T95's maneuverability and speed to perform the Circle of Death on large, slow tanks with heavy armor and heavy guns.
T-10 - A very, powerful tank at its level. If you can use it properly, and have it maxed out. The T-10 tops out at level 29, and at that level it has enough firepower to one-shot almost any tank it encounters. Unlike most tanks at this level, the T-10 also has enough armor to be able to withstand two, sometimes three shots from any tank's gun that it meets. This tank is highly recommended.
M42 Duster - Previously considered over powered the Duster is now considered as a support vehicle. As of 2.0 the Duster’s fire rate and damage has been gravely reduced. The vehicle can only fire AP and HE rounds, it is best to grind past the M42 as it does lead to the M56 scorpion.