How to lock UI elements position?

I have buttons and texts which are displayed at different positions at different devices and at different resolutions in GameMode.I have attached canvas scalar to canvas but it seems not to be working properly.Anybody suggest me the perfect way to have UI elements displayed at proper position.

you need to understand how anchors is used to adapt to different aspect ratios :
i suggests you read this official documentation : Designing UI for Multiple Resolutions

there is some useful YouTube videos also for example