Riga

Riga is the capital of Latvia.

Heading south

Towards Bauska, Kaunas, Vilnius

If you want to get towards the south it is best to get out of the city center first. Take tram number 10 towards ??? and get out at ???. You will see a gas station just around the corner. Asking people there is usually more successful than standing at the street.

Another possibility, from the city centre, taking a microbus to Kekava until the last stop and in Kekava you take the main road in the direction of Bauska.

Towards Jelgava

Cross the main bridge southwards, you can walk, but possibly there is a nice bus or minibus you can take. You keep on going until there is a crossroad with the A7 (not sure...) highway to Jelgava.