Combat Units
Riflemen- Riflemen are essentially the bulk core of the infantry. They engage the enemy with various weapons, but usually small firearms, and predominately rifles. Riflemen can use a wide variety of weapons, from machine guns, to marksmen rifles, to even sniper rifles, but in general their job is to provide accurate fire against the enemy, and suppressive fire when needed.
The general job a riflemen is the general job of any infantry unit. While they can use grenades, rifles, and a host of other weapons, their primary objective is to engage the enemy with their weapons, and to provide both accurate and suppressive fire.
Grenadier- A grenaider's job is primarily to engage their enemies with high explosives. These weapons tend to be destructive, and can break down installations, fortifications, or barricades. The weapons generally tend to have an area of effect and can incapacitate individuals in a given range, allowing for an area to be effected, or for lots of power to be delivered in a single area.
Due to the nature of explosives indirect fire is also possible. While a grenadier may function as an ordinary riflemen or even use the same weapons, ultimately their role is to provide high explosive power when needed.
Support- Support units primary role is to provide both heavy fire and suppressive fire. While this is not their only role, as they can function as riflemen, in general their objective is to provide consistent, heavy fire on the enemy, often suppressing them or allowing the unit to engage multiple enemies.
Heavier support units often times carry around heavy weapons, like large machine guns, while lighter support units might use a light machine gun, or a modified assault rifle designed for this position. In whatever the scenario, the support unit's goal is to provide heavy fire support to a squad or platoon. This can be in the form of lighter or heavier machine guns, but ultimately it is to serve as a force multiplier under the right conditions.
Team lead- While not really a position, it is often an extra unit to provide additional fire support to a unit. The unit's primary job is to direct or take in information to know how to respond or where to advance to; potentially strategist or provide tactics, or to relay information from command to troops, but ultimately to provide another unit to the team, and possibly lead by example.
While the unit in times does lead the troops, so far as issuing basic command goes, or relaying information, or assessing the situation, in general they are simply another addition to the squad, full-filling a role of standard infantry soldiers.
Auxiliary Units
Medics- Medics provide medical assistance to units. There is both a distinct medic corp and medical units integrated into squads and platoons. These units may operate independently or a part of the unit, depending on the situation.
Medics can receive general medical assessments to ascertain their levels of capabilities, but it is not required to be a medic. Still, it is advised you have some medical knowledge before becoming a medic.
Snipers- There are snipers attached to every platoon, providing both reconnaissance and direction action capabilities. Despite this, independent sniper platoons exist, providing substantial reconnaissance and capabilities to any unit. A standard sniper unit is comprised of their two snipers or a sniper and a spotter, or a 6 man team of a sniper, spotter, grenadier, 3 riflemen and an assault unit, usually carrying a machine gun. These units advance just as a typical firing team does, except their job is to clear a way for the sniper.
The riflemen often possess other capabilities, such as being a scout, medic, radio man, or demolition unit. Each of these units are responsible for the completion of the mission, and are often times sniper trained, as well. They generally understand how to achieve their goals and provide assistance to the primary sniper team.
These units are also frequently attached to a platoon.
Marksmen- Attached to every squad, these units provide more accurate or long range fire to every squad, allowing them to engage targets at considerable range, or take down highly specific target.
They are usually integrated into a fireteam, however they can operate independently if necessary.
Since each squad is expected to be a self contained unit, it is essential to have a marskmen in every squad.
Specialist- Demolitions, welders, general engineers, medics, radio operators, mortar units, heavy weaponry, anti-tank, anti-air, and other various units are within this category, although all units technically qualify as a specialist within their particular category and nearly all soldiers qualify as a specialist, or E-4, if not a commander of some kind.
Specialists often times provide highly specific jobs, for the scenario, such as being language translators, for that area, medics, map providers, UAV operators, provide heavy or specific weaponry (just as fence or barbwire cutting stuff), abilities to breach walls with explosives, or welding materials, or with standard door breaching rounds (such as in close quarters), among many other things.
Depending on the scenario, a specialists job may even change, as they may be intended to full-fill several specific jobs depending on the mission. This might make a specialist a more flexible job, or they may keep the same job. In any case, they are part of the integrated unit that forms a riflemen squad!