Question

Losing electrons means losing,gaining means to gain electrons,but what do you mean by sharing???​

Answer 1

It means that , in a chemical combination when the atoms of both the elements loose the e- equally then it is called sharing


For an example take Sodium (Na)
Electronic configuration = 2,8,7

Now , we have to combine two Na
But both required one e- to become stable .
Thus , none of the atoms will loose e- , they will share one e- each.

Thus, both of them loose one e-. Now, total no .of e- shared is 2.Thus, the formula is Na2.

Answer 2

Sharing electrons means to share the own electrons of and atom with any other atom  together like a carbon atom does (neither it loses electrons nor it gains electrons) it simply shares it's electrons with other atom like with oxygen by foming CO2.