First, The airport is located at the nor-east part of the city. The event is taking place at "UCA" (Universidad Centroamericana) which is in the center of the city. There are many hotels close to "la UCA". An usual trip in car inside the city last for about 5-10 minutes. However airport-center city is a longer route, and can take up to 40 minutes (depending on traffic).
There are no taximeter in Nicaragua so cabs prices are negotiate. Taxis from hotels and airport usually charge more because of their representation. Again, a trip inside the city can't cost more than 50-60 CS ( 1 US = 23 CS ). I do not recommend using buses since they are in bad mechanical shape and the routes are confusing. If you're going to travel on taxi, ask for the price before you get in and try to pay with the exact cost or with a bill close to it (ex : Do not pay a 50 CS trip with a 200 CS bill). Hotels and restaurants have no problems accepting dollars, however they will give you the change back in Cordobas (CS). Taxis on the other hand will often round down the dollar to 20 CS.
Health : Do not drink/eat anything from the street. You don't know what it is made from or the healthy measure. A local dinner on a food restaurant can cost from 40-150 depending on what you order. July is in the middle of the rain season, so mosquito's repellent and an Umbrella are advised. Local water is drinkable but I recommend mixing it with bottle water at least on the first day so your body get used to it.
Safety: Managua is a safe city, specially in the day and areas with high concentration of persons. It is safe to walk around the main areas, however double/triple check when crossing the streets since drivers (specially taxis and buses) are disrespectful towards pedestrians. As usual, grab your bag with precaution. If you don't know where you're going, ask for indication.
Here some basic Spanish :
Hello, my name is X // Hola, mi nombre es X.
How much does cost ? // cuanto cuesta ?.
I'm going to X // Voy a X.
No, thank you // No, Gracias.
Yes, please // Si, por favor.
Where can I take a taxi ? // Donde puedo encontrar un taxi ?
Do you speak English ? // Sabes Ingles ?