so essentially, every tire in F1 has a compound number
there's C1, C2, C3, C4 and C5
C1 is the hardest tire of the five and therefore the slowest on track, but it lasts the longest
C5 is the softest tire of the five and therefore the fastest on track, but it lasts the shortest
each number in between is like a transition
in each race weekend, a number range is picked for tires
(let's take C2, C3, C4 as an example)
C4 would be labelled the soft tire for that weekend, C3 the medium and C2 the hard
softs have a red ring, like 
mediums have a yellow ring, like 
and hards have a white ring, like 
there's also 2 wet tire compounds
(intermediate) is used on a damp track and
(wet) is used in heavy rain conditions
the reason we have 5 main compounds instead of 3 is due to the different tracks requiring more durable tires
for example, singapore's grand prix uses c1, c2 and c3 because it is a tight street circuit with demanding corners
if you have questions on a specific part of this ask me and i'll try to explain it better, this is kind of rushed