I am going to use the Iso-Area algorithm of the QNEAT3 plugin to generate Isochrones. I need to determine which parts of the road network are one-way and which parts are two-way. In the way that for example assign value 1 to the records in the attribute table of road layer that are one-way and assign the value 2 to the records that are two-way then feed the direction filed, value for forward direction, and value for backward direction with the related field and values. Is this a correct way to generate Iso_Areas based on the one-way and two-way road segments?
Yes this is the correct way of using the direction functionality in the QNEAT3 algorithms. You can use arbitrary values for one-way streets and two-way streets, you just have to tell the algorithm which values you applied in your direction field for which street type. For that, use the parameters exposed in the advanced section.