On the LTSpice toolbar, on the far right, click on the .sp icon.

In the box, type:

.inc 74hc.lib

Then click the OK button, and drop the line of text near your .tran statement (it can be anywhere in the schematic, but I usually put .inc statements near the .tran statement.)

I am also facing the same problem , i have downloaded the library 74hc, but still there are some errors, i wanna know how to fix the errors, please help me in this regard.. Thanks in advance !!!!

 

There are a lot of people who like to step on a rake. To step on a rake is a Russian expression. I mean, when you step on a rake, you get a grip on the forehead.
Install my library and you will have fewer problems. Read the manual and copy my library:
http://bordodynov.ltwiki.org/