Although ISO 45001 does not include requirements for lockout/tagout, this does come under the clause 6.1.3, determination of legal requirements and other requirements, as there are many locations which have legal requirements for lockout/tagout procedures. As this is the case it is important to know what your applicable laws about lockout/tagout procedures are so that you can design your procedures to meet the requirements. The legal documents will tell you when a lockout/tagout procedure needs to be put in place.
In general, the idea is that when a piece of machinery is having work done to it outside of regular production, such as maintenance, you have a way to make sure that it is safeguarded against start up so that employees are not injured during the maintenance. One common method of doing this is to have each employee who is working on the machinery have their own tag or lock which they put in place to stop the machine from engaging; and only that employee can remove their tag or lock. These often go on the start mechanism such as the electric panel of the equipment. So, if 4 people are working on a machine, there will be 4 individual locks in place and only once the last lock is removed by the last employee is the machine able to start. Since no one but the employee who put the tag/lock in place can remove it, you are certain that all employees are safely away before start up.