Large Finnish dictionaries contain information about word forms, as numbers referring to inflection patterns (paradigms). Bilingual dictionaries may lack such information, making things more difficult. You may therefore find the online service Joukahainen at joukahainen.puimula.org useful, although its user interface is in Finnish and somewhat clumsy. It accepts a dictionary form of a word as input (use the infinitive for a verb) and shows basic information about the word, including some inflected forms:
These forms show the basic variation in the stem of word and its suffixes. They can be used to generate other forms by following general principles, once you have learned them. For nouns and adjectives, almost all case forms are shown on request. The service does not cover pronouns and numerals.
For verbs, there is also Verbix.com, which generates all the normal forms of a verb.
The official Kielitoimiston sanakirja also contains inflection information. However, the information is largely implicit: it refers to inflection patterns. For verbs, it contains the same type words as Joukahainen and additionally the potential form, 3rd person singular (e.g. halunnee). For nouns and adjectives, eight forms are shown.