Hello Abilash,
To add two or more string variables together, use the "+" operator.
For example if you want to show net weight and unit (which are in individual columns) adjacently in a single column, write the below Javascript in Initialize event on the column where u want to show concatenated value.
this.rawvalue = this.parent.weight.rawvalue + this.parent.unit.rawvalue;
This will compute for each record in the Internal table because the code is directly on the column in the design level.