To add an extra charge to a job (if you want to apply a rush fee, for example), you have to click on the estimate of the job, on the left in the job details.
You'll arrive here:
To add an extra charge, click on the little pencil in the "Extra charge" column. The extra charge should be defined as a percentage. You can also add a description for this supplement (rush fee, weekend fee, etc.). When you add a description for the extra charge, a little "+" appears on the corresponding column, and the description is mentioned (in blue) below the name of the job:
In the documents you create, there is an "Extra charge" column. Please not that this column is always visible in the interface, but it won't appear in the PDF documents if you haven't defined any extra charges.
If you send you documents to your clients in another language (and if you have created another document configuration for this - see this article: http://help.lsp.expert/documents/can-i-translate-my-documents-in-another-language), you can translate the "extra charge" title by going to Settings > Document and email configuration > click on the configuration concerned > click on the Translations tab of this configuration. There you can translate the "extra charge" title in the language concerned.
If you would like to name your extra charge differently (for example if your only extra charge is "Rush fee" and you would like the column in your documents to be named "Rush fee" instead of "Extra charge" + a "Rush fee" description), click on the configuration concerned under Settings > Document and email configuration and go to the Translations tab of this configuration. There you can "adapt" the name of your extra charge.