I cant draw on the edges

1.- i draw a circle and extrude it , then i draw a circle on the face, expanding , it does well, however, now if i want to do a circle perforated. Over the face , i cant do that … so i need to use “subtract”. But i remember what the program before can do that , not now …

2.- i use solidworks and it have a option call “ convertir identidades “ en español , in ingles maybe is “convert indetities” . So i need this , because i click on the face and i can draw the same lines i can take new points over there . Shapr3d have “ desplazar en español” but is not the same , it have a offset of the line , not draw the same line .

3.- when i draw Something. That does not fall in the grid , if i want to take a reference, its and does not allow it , it would be ideal that when passing near the ends of the drawing i could take reference. ( look the picture ) … i never can click on the edges.