I mean to say if we compare strings then we use strcmp but its strncmp here and also "&" is used which isn't used usually...that's what i am asking if could make me understand the meaning of this line...if say char line.......& also why sscanf is used???
strcmp - compares 2 strings up to their zero terminator
strncmp - compares 2 strings up to a limit of either their zero terminator or a supplied count of characters. This is useful if you happen to want to look for a specific substring of characters within a larger string.
You don't just have an & you also have  which are important in this context. The entire expression is &line[j].
Assuming that line is defined something like char line;, strings are just arrays of characters there is nothing particularly special about them in C except that the last character must always be the NUL terminator '\0'.
In this case you are presumably used to calling strcmp like this
You need to understand what the expression line does in this case. When you use an array name without the  then the evaluated expression returns a pointer to the first item in the array and as a type of pointer to the type of the array, in the case of line this is char*. So is there any other way to get a pointer to the first item in the array? We case use  to access items in the array some line is the first item in the array. To get the address of the first item in the array we can use the address of operator which is & so &line also returns a pointer to the first item in an array, line and &line are functionally equivilent (they return the same thing, a pointer to the first item in the array).
Now compare &line to the expression you are interested in &line[j]. The only difference is that 0 is replaced j, the [j] selects the jth item in the array and as before the & gets the address of it so the expression &line[j] returns a pointer to the jth item in the array.
Putting it all together then in the statement if(strncmp(&line[j],"MEMBERED",8)==0) this gets a pointer to the jth item in line and calls strncmp to compare the first 8 characters found there with the string "MEMBERED" the result is tested ==0 and if the data in line matched the string the code in the if statement is exectuted (like strcmp strncmp returns 0 when it gets a match).