Create a template when no existing one answers your question, or when one is close but needs other columns. The quickest start is a copy of a template that already works.
In the side menu, select Reports > Create Report.
On the card of the template to start from, select the menu (three dots).
Select Save a copy, marked 3.

The copy opens in the builder, named "Name (copy)".
Change the name, then continue with step 5 of the next section, or go straight to Preview. Do not pick another source for a copied table: that replaces its columns.
In Reports > Create Report, select New template.
An empty builder opens with one table that reads the first source on your list.

In Template name, marked 1, enter a name, for example Long trips this week.
Optional: In Description, marked 2, enter one line that says what the report is for. It shows on the template card.
Under Data sources, marked 3, select the source, for example Trips.
The table fills with a default set of columns for that source.

Remove the columns you do not need with × on their chip. Add others with Add column, marked 4.
Optional: Under Group by, marked 5, choose a key such as Unit or Day to fold the records into one row each. See Group, filter and total report rows.
Optional: Select Add a chart to draw the table. See Report chart settings.
The validation bar under the name says "Template is valid", or lists what to fix.
Select Preview.
The Generate screen opens with your unsaved template.
Choose a period and units.
Select Generate Report.
The report appears with your columns.

Select Back, marked 4.
The builder opens again with your changes.
You cannot pin a preview to a dashboard or schedule it until you save the template.

If you select Back with unsaved changes, a dialog asks first. Discard changes leaves without saving.