Combine field in registration

Hi, I want to create a field for user registration where the actual value is composed of two other fields, a select and an input type=text,
Is it possible to do so?

You want to add them together or just displays their values together? If you just want to display the values together you can use substitutions inside of a Custom HTML field or use the layout parameters of either of those fields. See the below regarding substitution usage. You can find the layout parameters for fields under Parameters > Layouts while editing the field.

www.joomlapolis.com/documentation/279-community-builder/tutorials/18353-using-substitutions-throughout-cb

For example the below in a Custom HTML field would display the two fields next to each other.

[cb:userfield field="cb_country" /] [cb:userfield field="cb_state" /]

The below would be if using the Profile View Value Layout of cb_country.

[value] [cb:userfield field="cb_state" /]

Hi, I would like to add them together, not just displaying them, can you help me out?

Then you need CB Code Field or CB Query Field. Code field would let you do this with PHP and Query field would let you do this with SQL.