Clearly mark the part that was taken from another site and add the link to the source.
The best way to mark that part is to use the "quote" feature built into the editor. The link to the original source should be placed right above or below the quoted part. Make sure that you only quote the part that is relevant for your answer.
Characters with a loyalty skill bonus will gain skills as if they didn't have them, e.g. a knight with 100 base sword fighting (103 after loyalty bonus) will still gain skills as if they had 100 sword fighting.
The same goes if you decide to use any picture, screenshot, map, or image from another website. Always link to the original source.
Image of a player obtaining an achievement taken from tibia.fandom.com/wiki/Achievements
If you only use one or two Tibia sprites to e.g. visualize the item you are talking about, you may optionally skip the source. Tibia sprites do not belong to any of the fansites, but to CipSoft GmbH and the attribution of their work is already placed on every subpage of TibiaQA.
Avoid answers that are just copy-paste of other sources. Users usually ask very specific questions. While quotes from other sources can help, they are almost never a complete answer to the question. Make sure to take time to answer the question in the first place and then back your answer up with a link/quote to the trusted source.
If you spot an answer that seems to use the work of another fansite but isn't properly attributed (or at all), please flag it as Requires editing and explain that the answer does not properly attribute the work.
If you know the original source you can also include the link in the flag or in the comment, or even add it yourself (1500+ rep points required for editing answers). If you decide to add the necessary attribution yourself, it's still a good idea to notify the author of the post that he has not properly attributed the work of someone else so they can avoid that mistake in the future. A link to this guide can be shared with them as well!