Portuguese archer and, at left, a crossbowman, early 16th century
(Click image to enlarge)
In the sixteenth century, the basic tactical unit was the company. It consisted of a variable number of soldiers, usually around 50 though sometimes many more. They were commanded by officers: a captain, assisted by one or more lieutenants and an ensign to carry the flag. While senior officers generally came from the lower nobility, petty officers were drawn from the ranks of the more experienced or better-educated soldiers. These were the anspessades,(roughly the equivalent of modern lance-corporals or first-class soldiers) the corporals, sergeants and quarter-master sergeants. There was at least one drummer and often a fife player per company, as well as a "frater" whose duty it was to provide first aid to the wounded. Companies could be composed exclusively of pikemen, crossbowmen or harquebusiers, or of a mixture of these specialties. Apart from the names of certain ranks and from changes due to evolving weapons, the companies constituted five hundred years ago were similar in many ways to those of today. 
During the Renaissance, it was incumbent upon captains to recruit the men they needed to fill the ranks, although they could delegate this task to representatives - lieutenants or recruiting sergeants - who made the first approaches. When agreement was reached, the recruits found themselves bound to a captain by contract (which was sometimes oral), and they received a bonus paid to them at the time of their enlistment.
New recruits had to swear to abide by the Articles of War, which set forth their duties and obligations, especially loyalty to the flag, and warned of the consequences that awaited in case of mutiny or desertion - usually capital punishment. When soldiers received their pay, the captain would have already made certain deductions to cover the costs of their gear and weapons, if they did not have any. Officers usually made a profit on this transaction. Similar deductions were made for food and clothing. If, however, recruits arrived armed, equipped and dressed, various clauses in the contract would change to their advantage. Soldiers being sent overseas were apparently usually granted certain privileges to cover the cost of their gear, which amounted to a form of compensation.