Can someone please check my grammar

tildetdouspartI stepped on a thin plywood

I stepped on a thin piece of plywood

tildetdouspartlaying on the floor,

lying http://dictionary.cambridge.org/dictionary/english/lie o

tildetdouspartI stepped on a thin plywood laying on the floor, slipped and fell on the ground. I hurt my right knee, elbow and lower back

This is the foreground, the main event.

tildetdouspartI used that thin plywood as a gate between my stairs, so that my small dog will not go upstairs.

This is the background, information t

Thank you CJ and anonymous

You might also say it like this:

I tripped on a sheet of plywood on the floor and fell, hurting my right knee, right elbow, and back. The plywood was usually wedged between the railings of the stairs, to block access to the top floor so my dog couldn't go up there.

i tripped on the plywood sheet that was put at the bottom of the stairs to prevent my dog from going upstairs, and hurt my knee, elbow and lower back.