Hey there! Quite new to Pathfinder and played a few games but there are some things I'm not quite sure about the monster stats, when it lists, for example:

http://paizo.com/pathfinderRPG/prd/monsters/elemental.html
Small Earth Elemental
hp 13 (2d10+2)
Melee slam +6 (1d6+4)
Str 16, Dex 8, Con 13, Int 4, Wis 11, Cha 11
Base Atk +2; CMB +4; CMD 13

Are the HP and Melee Damage already taking its ability modifiers from Str/Con into consideration?

I'm quite confused about this, as it says Slam +6, but with BAB+2 and Str16 (+3) this should be +5, no? And the Damage at +4, ok but Str 16 is +3 modifier? And the Hp at +2 but CON 13 is +1 bonus

And then if I look at this other monster:

http://paizo.com/pathfinderRPG/prd/monsters/hyena.html#_hyena
Hyena
Init +2; Senses low-light vision, scent; Perception +7
Skills Perception +8

Why does it state +7 in the first line and then near the bottom of the stat block, it shows a +8? Why the +7 at all?

This is very confusing.
So, what am I missing?

Well for the elemental, there is an extra +1 from being small.

As for the hyena..... *shrugs*....Typo?

Hey there! Quite new to Pathfinder and played a few games but there are some things I'm not quite sure about the monster stats, when it lists, for example:

http://paizo.com/pathfinderRPG/prd/monsters/elemental.html
Small Earth Elemental
hp 13 (2d10+2)
Melee slam +6 (1d6+4)
Str 16, Dex 8, Con 13, Int 4, Wis 11, Cha 11
Base Atk +2; CMB +4; CMD 13

Are the HP and Melee Damage already taking its ability modifiers from Str/Con into consideration?

I'm quite confused about this, as it says Slam +6, but with BAB+2 and Str16 (+3) this should be +5, no? And the Damage at +4, ok but Str 16 is +3 modifier? And the Hp at +2 but CON 13 is +1 bonus

And then if I look at this other monster:

http://paizo.com/pathfinderRPG/prd/monsters/hyena.html#_hyena
Hyena
Init +2; Senses low-light vision, scent; Perception +7
Skills Perception +8

Why does it state +7 in the first line and then near the bottom of the stat block, it shows a +8? Why the +7 at all?

This is very confusing.
So, what am I missing?

Hyena is one of the many typos. There is an entire 3PP dedicated to fixing those errors.

As Kazarath says, the elemental gets +1 to attack for being small.

The additional point of damage is because a creature with only a single natural attack gets to add strength bonus times 1.5 instead of just strength bonus. With 3*1.5 being 4.5, and Pathfinder always rounding down, that becomes +4.

The HP is +2 because it has 2 HD. The CON modifier is added to each HD, just like it's added to each class level for a PC.

The Hyena perception discrepancy is a typo. 8 is the correct number (1 rank, +1 WIS, +3 class skill, +3 skill focus). The reason the perception is listed twice is because it's always listed as part of the "Senses" line, and all skills are listed as part of the "Skills" line.

Ah that does clarify things, thank you!
So many things to keep track of - like the size bonus/penalty I forgot to add!

Are the HP and Melee Damage already taking its ability modifiers from Str/Con into consideration?

Yes. Note that a few monsters (eg those with the rage abilities, or those that can cast buff spells) can change their ability scores. Try to avoid those.