@User: Use the menu

Edit->Text...

to create the labels. There are two kinds of labels, the original kind based on fixed-size X11 fonts, and rendered ones based on outline fonts that I added to magic some years back. The command-line invocation is complicated (have to provide font name, scale, rotation, etc.) so I usually just direct people to the menu item. With the rendered fonts, you can select the size of the text in microns. With the fixed-size X11 fonts, you get a handful of fixed pixel sizes, and when magic deems that the view is zoomed too far out, they disappear altogether, which is what you're seeing. To delete a label: Put the cursor box around the area where the label is, and type "erase labels". That's the best way to remove the label without touching anything else around it.

I added with edit>text tab , and increased the size to 10um (large i guess) but still not visible though. Am i missing anything ?

I'm not sure what you're getting, though. It doesn't look like a rendered font. I generated the picture below using a label 1um high, and as you can see from the measurement in the layout window, it's one micron high. Also, you selected "Port: enable" in the GUI window, and port labels should be rendered in blue.

What is happening is - i add text of 1um height , and it doesnt immediately show in the layout , i save and close the layout , then and repoen again to see jumbo texts (becuase of my text height chosen )