The First Click attribution model is a conversion attribution model by which the 100% of the conversion is assigned to the first campaign, medium or keyword that participated in the customer journey.
The first interaction or first click attribution model is not used by default in almost all the Web Analytics Tools, like Google Analytics. Normally the Analytics Solutions have a multi-touch attribution modeling reports, where you can compare different attribution models.
If you work normally with First Click Attribution Model your are giving 100% of the value of the conversion to the first click, as we said before; so the other channels are not taken into consideration or given importance. If you are a new brand, and nobody knows about your product, web or brand, this attribution model is really reflecting the reality of your company.
The fist click model is appropriate for conversions which are not impulse buying or you are not a well known brand, without branded traffic or direct traffic.
Other Multi-tocuh models: Last Click, Lineal, Decline over time, Based On Position…