Currency: The Afghani (AFN). Money changers operate openly in bazaars and offer better rates than banks. US dollars are widely accepted in Kabul and major cities. Bring cash -- international ATM cards do not work, and credit cards are not accepted anywhere outside a handful of Kabul guesthouses. Carry small denominations of both Afghanis and US dollars.
Language: Dari (Afghan Persian) and Pashto are the official languages. Dari is more useful for travelers as it is the lingua franca in cities. English is spoken by some educated Afghans in Kabul, particularly those who worked with international organizations, but do not count on it elsewhere. Learning a few phrases of Dari goes a long way: "tashakor" (thank you), "salaam" (hello), "lotfan" (please).
Visas: See Getting There for current visa information. Requirements are unpredictable and change frequently under Taliban governance.
Safety: Afghanistan is one of the most dangerous countries in the world for travelers. Kidnapping, armed robbery, unexploded ordnance and suicide attacks all remain real risks. Security conditions vary enormously by region and can change overnight. The north (Mazar-i-Sharif, Balkh) and west (Herat) have generally been calmer than the south and east. If you travel here, you need local contacts, a trusted guide and a willingness to change plans instantly based on the situation on the ground.
Women travelers: Under Taliban rule, women must be fully covered (including face) in public. Women cannot travel without a male guardian (mahram). Female foreign travelers face the same restrictions in practice. Solo female travel is not possible.
Communications: Afghan mobile networks (Roshan, Etisalat, MTN) work in cities and along major roads. Buy a local SIM card in Kabul. Coverage drops to nothing in rural and mountainous areas. Internet access is available in Kabul and major cities but is slow and unreliable.
Health: Medical facilities are extremely limited. Bring all medications you might need. Drink only bottled or purified water. The nearest reliable hospital for serious emergencies is in Pakistan or Dubai. Travel with comprehensive evacuation insurance if you can find a policy that covers Afghanistan.
Electricity: 220V, 50Hz. Power supply is erratic outside Kabul. Bring a headlamp and a power bank.