If you have reoccuring content which should be the same across multiple resources you can use a Chunk. Create a new chunk and add the chunk placeholder
[[$yourchunkname]] within the templates you want this content to appear.
If you want the content of this chunk to be adjustable by your client, you have to use a TV (Template Variable) which gets placed within your chunk. Because TVs are resource specific you can’t just use the general placeholder
[[*yourtvname]] as it would only show the values entered for the current resource.
However you can assign the TV to the template of a resource, let’s say your “Home” resource and reference that resource by using the fastField tag within your chunk. If your homepage has resource ID 1 it would look something like this:
[[#1.yourtvname]]. This will now fetch the data from your TV but always take the values entered in the “Home” resource.
In general I would highly recommend investing some time in understanding how the following are used and what their functions are which will unlock the full MODX flexibility for you:
Hope this helps!