Change biblatex citation style

Question

I am struggling to find the right settings of biblatex for my use case. Given the following entry in the .bib file

@article{einstein,
  author =       "Albert Einstein",
  title =        "{Zur Elektrodynamik bewegter K{\"o}rper}",
  journal =      "Annalen der Physik",
  volume =       "322",
  number =       "10",
  pages =        "891--921",
  year =         "1905",
}

I would like to have the following Output for \footcite[Vgl.][12--15]{einstein}

Vgl. Einstein (1905), S. 12 ff.

and an corresponding entry in the bibliography as follows

Einstein, A. (1905): Zur Elektrodynamik bewegter Körper, in: Annalen der Physik, Jg. 322 (10), S. 891-921.

I tried using authoryear as style and authoryear-ibid as citestyle (ibid is necessary) and they come close but I have to follow really strict specifications, so I need to change these styles. Unfortunately I have absolutely no idea where to start as this is my first time using biblatex. I looked for a solution in other threads but they all seem to be really specific to the respective problem so I can't seem to find a "general way" to change citation styles.

If anyone could tell me if there is an easy solution or point me to a tutorial where I can learn how to write or change styles that would be great!

Edit: Minimal working sample: sample.tex:

\documentclass[a4paper,12pt,oneside]{article}
\usepackage[ngerman]{babel}

\usepackage[
    backend=biber,
    style=authoryear,
    citestyle=authoryear-ibid,
]{biblatex}

\addbibresource{sample.bib} 

\begin{document}

Random sentence.\footcite[Vgl.][12--15]{einstein}

\printbibliography
\end{document}

sample.bib:

@article{einstein,
  author =       "Albert Einstein",
  title =        "{Zur Elektrodynamik bewegter K{\"o}rper}",
  journal =      "Annalen der Physik",
  volume =       "322",
  number =       "10",
  pages =        "891--921",
  year =         "1905",
}

Answer 1

\begin{advertisement}

For small tweaks like this the styles of my biblatex-ext bundle can be more convenient than the standard styles.

In particular the punctuation macros \jourvoldelim and \volnumdelim allow us to avoid having to redefine the two bibmacros journal+issuetitle and volume+number+eid.

\DeclareInnerCiteDelims gives us a quick way to wrap the year in the footnote citation into round brackets, something that would otherwise require redefining the cite or cite:labeldate+extradate bibmacros, which could clash with \textcite if done incorrectly.

Everything else in the code below is standard biblatex.

\end{advertisement}

The comments explain what each code block does, more can be found in the biblatex documentation and the biblatex-ext documentation.

\documentclass[a4paper,12pt,oneside]{article}
\usepackage[ngerman]{babel}
\usepackage{csquotes}

\usepackage[
    backend=biber,
    style=ext-authoryear-ibid,
    giveninits=true,
    uniquename=init,
    autocite=footnote,
]{biblatex}

% comma between bibliography units
\renewcommand*{\newunitpunct}{\addcomma\space}

% colon after Author (Year) in bibliography
\DeclareDelimFormat[bib,biblist]{nametitledelim}{\addcolon\space}

% no quotation marks around titles
\DeclareFieldFormat
  [article,inbook,incollection,inproceedings,patent,thesis,unpublished]
  {title}{#1\isdot}

% Journal, Jg. Vol (Num)
\renewcommand*{\jourvoldelim}{\addcomma\space}
\DeclareFieldFormat[article,periodical]{volume}{\bibstring{jourvol}~#1}
\DeclareFieldFormat[article,periodical]{number}{\mkbibparens{#1}}
\renewcommand*{\volnumdelim}{\addnbspace}

% parentheses around year in footcite
\DeclareInnerCiteDelims{footcite}{\bibopenparen}{\bibcloseparen}

\addbibresource{biblatex-examples.bib}

\begin{document}
Random sentence.\autocite[Vgl.][380\psqq]{sigfridsson}

\printbibliography
\end{document}

As Andrew Swann mentions Guidelines for customizing biblatex styles is a great starting point for common and easy modifications, but you can find many more complicated customisations on this site if you search for specific terms. A few of the biblatex tutorials listed in biblatex in a nutshell (for beginners) have a short "common customisation" section or mention a few common modifications. Other than that you can find out what macro to modify and which field format to tweak by looking at the source of your style (biblatex.def, biblatex.bbx and <bibstyle>.bbx, <citestyle>.cbx).