The researchers defined 4 levels of technology proficiency, based on the types of tasks users can complete successfully. There was a very good summary published here (https://www.nngroup.com/articles/computer-skill-levels/) and excerpted below.
For each level, here’s the percentage of the population (averaged across the OECD countries) who performed at that level, as well as the report’s definition of the ability of people within that level:
"Below Level 1” = 14% of Adult Population
Being too polite to use a term like “level zero,” the OECD researchers refer to the lowest skill level as “below level 1.”
This is what people below level 1 can do: “Tasks are based on well-defined problems involving the use of only one function within a generic interface to meet one explicit criterion without any categorical or inferential reasoning, or transforming of information. Few steps are required and no sub-goal has to be generated.”
An example of task at this level is “Delete this email message” in an email app.
Level 1 = 29% of Adult Population
This is what level-1 people can do: “Tasks typically require the use of widely available and familiar technology applications, such as email software or a web browser.
There is little or no navigation required to access the information or commands required to solve the problem. The tasks involve few steps and a minimal number of operators.
The reply-to-all task described above requires level-1 skills. Another example of level-1 task is “Find all emails from John Smith.”
Level 2 = 26% of Adult Population
This is what level-2 people can do: “At this level, tasks typically require the use of both generic and more specific technology applications. For instance, the respondent may have to make use of a novel online form. Some navigation across pages and applications is required to solve the problem. The use of tools (e.g. a sort function) can facilitate the resolution of the problem. The task may involve multiple steps and operators.
An example of level-2 task is “You want to find a sustainability-related document that was sent to you by John Smith in October last year.”
Level 3 = 5% of Adult Population
This is what this most-skilled group of people can do: “At this level, tasks typically require the use of both generic and more specific technology applications. Some navigation across pages and applications is required to solve the problem. The use of tools (e.g. a sort function) is required to make progress towards the solution. The task may involve multiple steps and operators. Integration and inferential reasoning may be needed to a large extent.
The meeting room task described above requires level-3 skills. Another example of level-3 task is “You want to know what percentage of the emails sent by John Smith last month were about sustainability.”
Can’t Use Computers = 26% of Adult Population
The numbers for the 4 skill levels don’t sum to 100% because a large proportion of the respondents never attempted the tasks, being unable to use computers. In total, across the OECD countries, 26% of adults were unable to use a computer.
That one quarter of the population can’t use a computer at all is the most serious element of the digital divide. To a great extent, this problem is caused by computers still being much too complicated for many people.
Let that phrase sink in: across the OECD countries, 26% of adults were unable to use a computer. In some countries like Japan, the number is even higher (about 1/3 of Japan's population can't use computers, which may reflect the aging population, poor interface design, or some other factor.)