Set in and out points using keyboard shortcuts Alt/Option + [ or ] for in and out.
Split layer at the CTI by pressing Ctrl/Cmnd + Shift + d
Type keyboard shortcuts in the Search Help field to locate many other useful shortcuts and techniques that any AE user should know.
Is there any way of making it in the same layer?
No. You can do it in Premiere though. The stuff you're talking about sounds an awful lot like video editing. AE is not a video editing program. That kind of thing is much faster and easier in Premiere.
As Rick says, you can press CTRL/CMD+Shift+D to split a layer. You can then either trim the layer or move it to be a second further ahead, but it will be on a new layer. Alternatively, you could use hold keyframes on opacity to keep it on the same layer.