Artifacts have two effects:
- Gives a stat boost as shown on the artifact itself. Usually a boost to things like HP, defense, attack, etc.
- A group bonus is given if you have two or 4 of a specific set. For example, having 2 of the “martial artist” set equipped to the same character gives them a boost to their physical attack damage on top of amy boost from the separate artifacts.
You can also level up am artifact by using other artifacts you don’t want as material. Leveling up an artifact raises the stat boosts it gives individually (but does not improve the set bonuses). A high rarity artifact can be leveld up further than a lower rarity (for example, a 4 star artifact maxes out at 16 while a 5 star maxes at 20) so a high rarity is typically better since it can have higher stats when fully leveled. If you haven’t already, just try seeing fi amy artifacts have a set bonus that looks like it would work well on a character and then see if you have more of the same set to equip them with, followed by leveling up those once equipped.
For example, Keqing has a naturally high critical hit rate, so artifacts that boost her crit rate even further or her crit damage (the multiplier her damage gets when she gets a critical hit) are typically considered good for her. She also has a pretty high “energy recharge” stat, so artifacts that can raise her recharge can also be quite powerful for her, since it means you would nearly be able to spam her ultimate skill.
For building your team, people usually focus on fulfilling a few specific roles:
- DPS, a character that can do a lot of damage quickly. Both Keqing and Tartaglia are pretty good at this, but Keqing is a bit better when on her own.
- DPS support, a character that can raise the offense power of your main DPS character. Tartaglia actually has a passive skill that raises the attack stat of everyone in your party, so he can double on this as well. That said, most 4 star rarity characters can fill this role quite well, most notably Fischl.
- Defense, usually a character that can use a shield of some kind. 4 stars that can be useful for this include: Xingqiu, Xinyan, Diona and any geo element character.
- Healer, can restore HP to allies. Of the 4 stars, Barbara is almost universally considered the best as she is the only dedicated healer of the 4 stars.
- Elemental synergy, characters that have elements that combine well with other characters you are already planning to use, such as the DPS character. For example, if your DPS is electro, having a character that can use hydro, pyro or cryo can be quite a useful combo as they let you do more damage using reactions.