Guys here is a very brief but I hope clear, overview of the period..
The main contests in Europe were between the mighty French under Louis XIV, the powerful Habsburg Austrians and the rich Dutch. The French wanted to expand France on its northern and eastern fronts. The Dutch wanted to protect their very profitable commercial interests. The Austrians were distracted by the pressure from the feared and giant Ottoman Turkish empire. The Austrians allied with the Dutch and others to try and contain the meglomaniacal tendencies of Louis.
Some people,particularly in UK portray the wars as religious wars between Catholics and Protestants. Although religion has some influence it is too simple and just plain wrong to portray it as a religious struggle.
Catholic Austria fought together with Protestant Holland against Catholic France. The Wars were mainly about commercial power, territory and dominance of Europe.
Theatres of operation
Mainly Flanders but also the Rhine, Italy, Ireland and Scotland. Peripheral, associated and non connected struggles in Scandinavia, Turkish front of southern Europe and elsewhere including Canada.
Formal, permanent armies were just beginning. There was little standardization of equipment, dress, tactics and formation.
The majority of each army was infantry (called FOOT). These were about 66% of the army.
The cavalry(called HORSE) were about 33% of the army. Also included within the horse were the Dragoons (MOUNTED INFANTRY). The can fight on foot or mounted (less good in both roles than the FOOT or HORSE but versatile)
Artillery has military gunners but civilian drivers and labourers. The guns were large, heavy and almost impossible to move in battle.
All troops wore long coloured coats with large turned back cuffs often of a different colour. The waistcoat underneath was usually an 'old coat' with the sleeves cut off. The trousers and socks could also be of different colours. Most soldiers wore a black felt hat with yellow or white lace around the brim and some coloured ribbons around the crown.
Coats colours could be red, blue,white, grey, brown, green, yellow, purple. Any variarion of the above in terms of shade(dark or light). The cuffs, waistcoat, trousers and socks where sometimes the same or a combination of 'different'. You will find many versions here
Look through these galleries and you'll see examples of everything mentioned so far.
Range from small (a few battalions) to enormous(perhaps 100 battalions per side with proportional cavalry... a lot!)
Hopefully this will get you started!