You need to get yourself a good basic SW test kit. Something that will test for ammonia, nitrites, nitrates, pH, and alkalinity. Most manufacturers sell kits like this. You should also get a good book, better to read up now than lose lots of fish and money. Once you test water, you want
ammonia=0,
nitrites=0,
nitrates >20mg/l,
pH@8.0-8.3
but most importantly READ READ READ!!