>>>
@Scepticalscribe a quick explanation: cantrips are spells that you can cast whenever and wherever you want. There's almost no drawbacks to using them. They're the weakest of the spells, however (level 0). Non-cantrip spells (spells that are levels 1 and above) must be prepared (more later, but currently you have two slots for prepared spells, but you have none at the moment (despite what others have said). You will get an opportunity to prepare spells shortly.
Clutching her side to stop the blood seeping from the scimitar wound, Syllin thrusts her other hand towards the screeching goblin holding its shield over its head as Bartolomeus prepares for a second strike with his greatsword. As she shouts an incantation, a white ray shoots out of your hand, freezing the very air around it --
*** CHECK ***
Since this is a direct attack, you'll need to beat the goblin's 14 AC. It's your proficiency modifier plus your spellcasting ability modifier (intelligence in your case, since you're a wizard -- a cleric would use his wisdom) plus a roll of a d20. Also, since you have disadvantage due to being less than five feet away from the goblin when casting a ranged spell (which the ray of frost is), you have disadvantage, so:
Syllin: 2 + 3 + 8 = 13 - fail
Syllin: 2 + 3 + 12 = 18 - success
Since this is a disadvantaged throw, your attack fails.
*** CHECK ***
-- and it squarely hits the goblin's shield, freezing it. Screaming obscenities, the goblin throws aside the frozen shield just as it begins to freeze its arm. It screeches and prepares to attack.
Simultaneously, Veit screamed as he swung his warhammer once more at the goblin facing both him and Claus --
*** CHECK ***
Same as before:
Veit: 2 + 2 + 7 = 11 - fail
Veit fails to hit the goblin.
*** CHECK ***
-- another *WHACK!* as the warhammer hits the goblin's shield just where Claus' sword has hit a instant prior. Screeching, the goblin rushed in for a counterattack --
*** CHECK ***
Since Veit has a AC of 18:
Goblin: 4 - 1 + 9 = 12 - fail
The goblin fails to hit Veit
*** CHECK ***
-- the scimitar once again bounces off Veit's armor, barely forcing a grunt out of the hardy dwarf;
The goblin facing Bartolomeus quickly disengages from battle and rushes the more vulnerable Syllin --
*** CHECK ***
Syllin has an AC of 12:
Goblin: 4 - 1 + 4 = 7 - fail
The attack fails.
*** CHECK ***
-- somehow the goblin missed the leg of the wizard's dead mare sticking out in its path. It tripped and and its scimitar struck only air;
The longbow-wielding goblin in the woods fires off another shot towards Syllin, not content with killing her mare --
*** CHECK ***
Syllin, again, has 12 AC, so:
Goblin: 4 - 1 + 16 = 19 - success
The attack obviously succeeds, so 5 damage is dealt. Syllin now has 0 hp.
*** CHECK ***
-- the world darkens as Syllin's consciousness fled the battlefield. She falls to the ground next to her departed mare.
>>> it is now ROUND 3.
@Moyank24 once more rolls for her fate:
*** CHECK ***
As you recall, >10 is success, <10 is fail:
Portia: 5 - fail
Portia now has 2 fails. One more and she will die permanently.
*** CHECK ***
>>>
@Don't panic you're up. As you recall, there's a goblin slightly behind you facing Syllin's body (its back is turned to you, so you have advantage), and there's a goblin unseen by you in the woods battling Veit and Claus, and of course the goblin in the woods shooting arrows. What do you do?
>>>
DM'S NOTE: Thanks to Don't panic's clarification, I've decided to disallow initiative swapping from now onwards.