How to use WHERE condition when using ON clause
You can put the filter in your join like this: 

SELECT Users.[Name],Users.[JobTitle],Users.[Active],Skills.[Qualification],
WeekTimeslip.[date_week],WeekTimeslip.[Company],
Project.[Billable],WeekTimeslip.[totalhours],
Utilisation.[utilisation]
FROM [master].[dbo].[Users] AS Users
LEFT JOIN [master].[dbo].[Skills] AS Skills
    ON Users.[Name] = Skills.[Name] AND Users.[Active] = '1'
LEFT JOIN [master].[dbo].[TIMESLIPS_wk13] AS WeekTimeslip
    ON Users.[Name] = WeekTimeslip.[employeename] AND Users.[Active] = '1'
LEFT JOIN [master].[dbo].[Project] AS Project
    ON WeekTimeslip.[Project] = Project.[Project]
LEFT JOIN [master].[dbo].[Utilisation_wk13] AS Utilisation
    ON Users.[Name] = Utilisation.[employeename] AND Users.[Active] = '1'
ORDER by Users.[Name]


Or just put it in a where clause like this: 

SELECT Users.[Name],Users.[JobTitle],Users.[Active],Skills.[Qualification],
WeekTimeslip.[date_week],WeekTimeslip.[Company],
Project.[Billable],WeekTimeslip.[totalhours],
Utilisation.[utilisation]
FROM [master].[dbo].[Users] AS Users
LEFT JOIN [master].[dbo].[Skills] AS Skills
    ON Users.[Name] = Skills.[Name]
LEFT JOIN [master].[dbo].[TIMESLIPS_wk13] AS WeekTimeslip
    ON Users.[Name] = WeekTimeslip.[employeename] 
LEFT JOIN [master].[dbo].[Project] AS Project
    ON WeekTimeslip.[Project] = Project.[Project]
LEFT JOIN [master].[dbo].[Utilisation_wk13] AS Utilisation
    ON Users.[Name] = Utilisation.[employeename]
WHERE Users.[Active] = '1'
ORDER by Users.[Name]


Usually, SQL will generate the same execution plan and the optimization process will do pretty much the same thing.