Can astrology predict or declare one's destiny like the future career or future spouse of a person? What is the role of free will of a person with respect to astrology?
Yes it can tell past, present and future. I am quoting Bhrigu Sutras about signification of houses:
First House (or Lagna-Ascendant) - Physical stature, colour, form and shape, constitution, health, vitality and vigour, natural dispositions and tendencies, personality and struggle for life, honour, dignity, prosperity, general well being, head, upper part of the face, virtues, longevity, start in life and an idea about the general structure of life.
Second House - Money matters, fortune, profit, gain or loss, one's power and resources, worldly attainments and possession of extrinsic value, jewellery, precious stones, bonds, securities and shares, speech, vision, right eye, memory, imagination, nails, tongue, nose, teeth, chin, family members. This is also a house of death or maraka sthana. Many a learned are of the opinion that education is also a signification of this house etc.
Third House - Mental inclination, ability, memory, intellect, inclination to study, courage, firmness, valour, prowess, heroism, younger brothers or sisters, cousins, neighbours, short travels, communications such as railways, wireless, posts and telegraphs, correspondence, writings, change of residence, signing contracts or agreements, rumours, carrying tales, hands, throat, shoulder blade, collarbone, arms nervous system.
Fourth House - Mother, one's home (native place), residence, domestic environments, grave, private affairs etc., secret life, vehicles, fields, pastures, farms, orchards, mines, buildings, ancestral property, hidden treasure, academic education, wells, water, milk, rivers, lakes etc.
Fifth House - Progeny (children), inclinations, pleasure, artistic talent, recreation, amusement, sports, romance, competitive activities like cards, crosswords, lottery, gambling or betting, love affairs, ambassadors, good or bad morals, mantra-tantra, religions mindedness, high learning and wisdom, intelligence, enormous riches, spiritual practice etc.
Sixth House - Sickness, diseases, nursing, food, service, employees, subordinates or servants, debts, cattle, tenants, enemies, maternal uncle, miserliness, intense anguish, litigation etc.
Seventh House - House of union or earthly ties, legal bondage, partner in life (wife or husband), partner in business, conjugal life, influence in foreign countries and reputation achieved there, sexual life, marital relations, danger to life, marakasthana (house of death).
Eighth House - Longevity or span of life, also called house of death (because end of longevity is death); inheritance, legacies, wills, insurance, pension and gratuity, accidents, death by drowning, fire or suicide; misery, misfortune, sorrow, strife, worries, disgrace, delay, dejection, disappointment, defeat, loss and obstruction, theft, robbery, chronic diseases.
Ninth House - Faith, wisdom and divine worship; fortune or luck (bhagya), philosophy, religious and philosophical beliefs, meditation, intuition and forethought, places of worship, sacrifices and charity, father, preceptor (Guru), teaching, Dhanna, grandchildren, dreams and visions, knees; communication with spirits, long journeys, voyage, air travel, higher education, foreign travel.
Tenth House - Thighs, honour, dignity, public esteem, name and fame, power prestige, credit (for good work and conduct), success and status, rank and renown, respect and reputation, ambition and authority, worldly activities, responsibilities, permanency (in service), promotion, advancement, appointment, profession, last rites to one's parents, religious functions. Government, high position such as President, Prime Minister or Minister, pilgrimage to holy places, honour from Government.
Eleventh House - Friends, society, community, favourites, ambitions, wishes, desires and their fulfilment, gains of wealth, success in undertakings, incoming wealth, profits, prosperity, elder brothers and sisters, recovery from illness, dawn of fortune, ankles.
Twelfth House - Loss and impediments, restraint and limitation, waste and extravagance, expenses, drudgery and deception, investments, donations, charities, separation from family, going to far away places, sorrow and sin, misery and misfortune, poverty, imprisonment, secret enemies, confinement in hospital, association, fraud, scandal, disgrace, secret sorrows, success through occult affairs, the feet, the left eye, the left ear, comforts of bed, debts, life in a foreign place and Moksha (final salvation).
Each planet has its own qualities and it depends which of the above houses it is placed in, and what its relations are with other planets in these houses. Time period also matters for prediction.
There are 2 kinds of events - those that can be changed and those that are fixed (honi). In Hindi it is said "जो होना है वो होना है".... But also it is said "Bhagyam falati sarvatra, na cha vidya na paurusham" or knowledge & efforts bear no fruit.... only destiny bears fruit