A saving throw represents your resistance to a spell, trap, poison, disease, or other similar threat. Depending on the type of saving throw you make, you need to use a different ability modifier. For example, a Dexterity saving throw requires a Dexterity modifier. Also, classes give you proficiency with certain saving throws, so you can add your proficiency bonus when making those types of saving throws. The formula for a saving throw is: d20 + saving throw ability modifier + proficiency bonus.
If your saving throw is greater than the save’s difficulty class (DC), the saving throw succeeds. Most saving throws halve (or sometimes reduce) the damage you take and protect you from some other negative effects (such as control).
When you cast a spell that requires a saving throw, your target makes a saving throw against your spell save DC.
Your spell save DCs will all be based on your spellcasting primary attribute, not your opponent’s save attribute!
The formula for the spell save DC is: 8 + primary ability modifier + proficiency bonus.
For example, if your primary attribute modifier is 3 and your proficiency bonus is 2, then your spell save DC is 8+3+2=13.
If your spell requires the opponent to make a Dexterity saving throw, then his d20 + Dexterity modifier + Proficiency modifier must be greater than 13 for the saving throw to succeed.
When an attack hits, or a spell deals damage, you need to determine the damage.
The damage determination is not complicated, and is often a simple XdY. (For example, 1d6 represents a roll of a 6-sided die, and 2d8 represents two rolls of an 8-sided die).
Some damage will allow you to add certain attribute modifiers, such as weapon attacks. (Weapons that hit based on Dexterity can add Dexterity modifiers to damage.)
For example, the damage of a light crossbow is 1d8 + your Dexterity modifier.
Damage can have different properties. Some monsters will be resistant to certain properties of damage (half damage, rounded down), while others will be vulnerable (double damage, rounded down).
If a monster has double resistance to a certain damage, the resistance will only be counted once. For example, if Monster A is resistant to both fire and spell attacks, then when it is hit by a fire spell, the damage will only be half. Therefore, the caster can prepare as many types of damage as possible to break through the enemy’s weaknesses.
A critical hit doubles the damage dice, so a 1d4 damage critical hit becomes 2d4.
Then add the attribute adjustment value, note that the adjustment value is not doubled.
For a profession like a thief, you must try to use sneak attacks, flanking attacks, etc. to gain advantages, making it easier to deal extra damage and heavy blows. The extra damage from multiple attacks can unleash extremely high combat potential.
Attack: An attack that requires a roll to hit, which is compared to the target’s AC. The higher the number, the better.
Immunity: To resist a certain spell/trap/emergency, you need to compare it with the DC of the spell/trap you want to resist. The higher the value, the better.
Difficulty Class (DC): How difficult it is to accomplish something. The higher the value, the harder it is.
Armor Class (AC): The value used by the character to defend and avoid attacks. The higher the value, the better.
XdY: X Y-sided dice. 2d8->2 8-sided dice.
Skills: A character’s abilities in various aspects, used for verification, such as sports, stealth, medicine, and history.
Long Rest: A rest lasting 8 hours, which will restore you to full health and refresh the cooldown of basically all spells, items, and abilities.
Short Rest: A short rest will restore a certain amount of health and refresh some abilities.
Prepare spells: Memorize some spells before resting so that you can use them the next day.
Level: The level and number of spells. Using all 2nd level spells means that you can no longer cast 2nd level spells before resting.
Proficiency: Indicates whether you are good at something. Proficiency in something can often give you a proficiency bonus.
Sub-job: a branch of a profession.
Concentration: Some continuous spells require concentration to remain effective. They may be disconnected when taking damage, and some controls can also force the concentration to be disconnected.
Advantage: If you have advantage on a check or an attack, you roll the d20 twice and take the higher result.
Disadvantage: If a check has disadvantage or an attack has disadvantage, you must roll the d20 twice and take the lower result.
Resistance: Damage taken from enemies with resistance attribute is halved.
Vulnerable: Double the damage taken from enemies with the Vulnerable attribute.