The easiest way to apply for a study program in Sweden is to use www.studera.nu. This website is run by the Swedish Council for Higher Education, which is the government agency that handles admission to higher education programs in Sweden. Admission is based primarily on your final grades from upper-secondary education.
The Swedish Council for Higher Education Services also assesses foreign secondary qualifications. Thus, a foreign grade from an upper-secondary school/equivalent can qualify you for higher education in Sweden. Swedish proficiency at the upper-secondary level is often also required.
If you lack any qualification for higher education in Sweden, such as a grade in Swedish, you can study to obtain the qualification through Komvux (adult education centre). Contact Komvux in your municipality to learn more about how to supplement your upper-secondary studies. You can find more information on different ways to learn Swedish under "Learning Swedish".