The principles

• Riba (interest) is prohibited, both paying and charging it, and the Quran's language about it is among its strongest (2:275-279). Money may not breed money; wealth should come from work, trade, and shared risk.
• Income must be halal: earned without deception, exploitation, or trading in the prohibited (alcohol, gambling, etc.).
• Wealth is a trust, not a scoreboard: zakat purifies it yearly, extravagance and miserliness are both criticised, and the beggar has a stated right in your surplus (Quran 70:24-25).
• Contracts are sacred: "O you who believe, fulfil your contracts" (5:1). Paying debts and keeping agreements is worship.

The honest answers to the hard cases

Bank accounts. Use a current account normally; either choose an account that pays no interest or give away any interest received to charity (without counting it as your own sadaqah). Islamic banks and windows exist in most Western countries now.

Mortgages. The genuinely hard one. Islamic home-purchase plans (ijara, murabaha, diminishing musharaka) exist in the UK, US, and elsewhere and are the first stop. Some contemporary scholars have permitted conventional mortgages for a primary home where no viable alternative exists, citing necessity; others firmly disagree. Do not let anyone give you a one-line answer; ask a qualified scholar about your actual situation, and don't let the mortgage question keep you from the religion. Renting is not failure.

Student loans. Similar territory: income-contingent loans (like the UK's) are viewed more leniently by some scholars because of how repayment and write-off work; classic interest-bearing loans are the usual ruling. Investigate national guidance for your country.

Pensions and investing. Very doable: halal pension funds and ETFs screen out interest-based finance, alcohol, gambling, weapons, and companies with excessive debt. Most large providers now offer an Islamic/Sharia fund; switching is often a single form. Day-to-day investing in ordinary shares of halal businesses is fine; interest-bearing bonds are not.

Insurance. Where required by law or genuine need (car, home, health), mainstream scholarship permits it; takaful (Islamic mutual insurance) is preferred where available.

The habits that matter more

It's easy to disappear into fiqh questions and forget the actual Islamic money culture: pay people on time ("give the worker his wages before his sweat dries"), don't buy what you can't afford, keep debts few and repaid, give quietly and regularly, and audit yourself yearly with zakat. A Muslim with a boring, honest financial life has already succeeded at most of this chapter.

Nobody sorts all of this in month one. Sequence it: zakat awareness now, bank account soon, pension fund switch when convenient, and the mortgage question when it's actually live.