16F88 Analog In

[skimask]

I soldered RB4-7 parallel so it doesn´t matter which of those is my analog input.

Ya...that'll help...

the only thing I don´t know is how to tell my 16F88 which input to use as analog in. And I don´t know why I need to set 3 registers for this, or even more.

Probably because the datasheet for that particular PIC tells you what you need to set and where to set it and how to set it to do what you need to do. PBP is good, but sometimes it's not the 'Do-All, End-All', Holy Grail, for everything.

I´m now below even this state because I can´t get my analog in to work without my 12F675.

Seems to be an ongoing problem.
Different problems in different areas, most seemingly related to problems with reading/understanding (mostly initially reading) the datasheets for the particular PIC you are using.
PIC#1 (be it whichever type) is very similar to PIC#2 (whichever type)...
But by no means are they always equal...sometimes they're not even close.
The 'F628A that you were using is close to the 'F88, but the 'F88 is much newer, with more options in some areas, and, for most practical purposes, the 'F88 isn't even close to the 12F675. They're different families. Basic bare-bones code written for one, will most likely execute on the other without a problem. But once you get into the internal modules of the PICs, register locations change, register names change, register functions change, even bit positions can change.

Go to Microchip.com, download the latest datasheets for the PICs you are using, and skim thru them.
Bookmark the pages with registers and functions you are interested in and READ them, comprehend them, play with them.